HOUSTON – Emergency teams – aided by a growing contingent of citizen-rescuers – used boats and waded through waist-deep water Monday seeking people stranded by devastating, historic flooding in the wake of Hurricane Harvey, even as forecasters warned of looming rain, rising rivers and floodwaters that would swallow still more streets and neighborhoods.

Even as the storm had been blamed for several deaths, the full toll of Harvey’s destruction remained unclear in Houston and across Texas and Louisiana. Officials warned that the danger was far from over, saying that flooding in Texas is unlikely to recede quickly and that the storm will force more than 30,000 people from their homes.

“We are not out of the woods yet,” Elaine Duke, the acting Homeland Security secretary, said during a Monday morning briefing in Washington. “Harvey is still a dangerous and historic storm.”

Fears also grew beyond Texas, where the floodwater pounding this city and others was measured in feet, not inches. President Donald Trump on Monday declared “emergency conditions” in Louisiana, where forecasts have called for as much as two feet of rainfall in some areas.

Louisiana Gov. John Bel Edwards, D, had asked President Trump for an emergency disaster declaration, similar to one signed for Texas last week, saying that Harvey posed a “serious danger to life and property” in the state, which is just a year removed from a massive flood disaster.

The immediate focus for many remained Houston, the country’s fourth-largest city and a sprawling metropolitan area, which faced dire circumstances and National Weather Service forecasts warning of more heavy rainfall.

Two reservoirs were opened to release water to relieve the stress the downpour has caused in the region, which has seen as much rain in a few days as it averages in an entire year.

“We are seeing catastrophic flooding, and this will likely expand and it will likely persist as it’s slow to recede,” Louis W. Uccellini, the NWS director, said at the Monday morning briefing.

Parts of Harris County, which encompasses Houston, were pelted with 30 inches of rain in the past 72 hours, the NWS reported early Monday.

Authorities had fielded scores of calls for help throughout the night from people stranded by water, although many areas had imposed curfew overnight Sunday in hopes of cutting down on the number in need of being rescued from vehicles. Help was pouring in from swift-water rescue teams from around the country.

Police in Houston dispatched officers on boats that were sent through streets where the floodwater reached the pumps at gas stations, and officials said they had conducted waves of rescue operations. While urging residents to stay off the roads, police have asked people with high-water vehicles and boats to assist in rescue efforts.

Across this city and suburbs many miles away, families scrambled to get out of their fast-flooding homes. Rescuers – in many cases neighbors helping neighbors – in fishing boats, huge dump trucks and even front-end loaders battled driving rains to move people to shelter. Some used inflatable toys to ferry their families out of inundated neighborhoods, wading through chest-deep water on foot while the region was under near-constant tornado watches.

The Brazos River, which runs southwest of Houston, is expected to reach record heights in the coming days. National Weather Service models showed the river rising to 59 feet by Tuesday, topping the previous record of 54.7 feet.

“A flood of this magnitude is an 800-year event, and it exceeds the design specification of our levees,” Fort Bend County Judge Robert Hebert said in a statement Monday.

The National Weather Service predicted that parts of Texas could receive nearly 50 inches of rain, the largest recorded total in the state’s history. It also warned that Harvey’s relentless downpours were expected to continue until late in the week and that flooding could become much more severe.

More than 82,000 homes were without electricity in the Houston area by Sunday night as airports shuttered and hospitals planned evacuations.

“We have not seen an event like this,” William “Brock” Long, administrator of the Federal Emergency Management Agency, said Monday morning at a news briefing. “You could not draw this forecast up. You could not dream this forecast up.”

Thousands of rescue missions were launched across Texas, and Gov. Greg Abbott, R, said Sunday that more than 3,000 national and state guard troops had been deployed to assist with relief efforts. An additional 1,000 National Guard members will be sent to Houston on Monday, Abbott announced late Sunday.

The Federal Emergency Management Agency said federal agencies have more than 5,000 employees working in Texas, and the White House said Trump plans to visit parts of the state on Tuesday.

The devastation that evoked Hurricane Katrina in New Orleans was also reverberating around the world from the Houston area’s large international community. In India, foreign minister Sushma Swaraj posted a tweet Monday saying 200 Indian students were “marooned.”

“They are surrounded by neck deep water,” she wrote.

Officials said Houston, a major center for the nation’s energy industry, had suffered billions of dollars in damage and would take years to fully recover. Oil and gas companies have shut down about a quarter of their production in the Gulf of Mexico. Spot prices for gasoline are expected to jump on Monday, but the full extent of damage will not be clear for days, companies and experts said.

Harvey’s sheer size also became apparent Sunday as heavy rains and flooding were reported as far away as Austin and even Dallas. What started with a direct impact on the tiny coastal town of Rockport on Friday night turned into a weather disaster affecting thousands of square miles and millions of people – with no clear end in sight.

In Austin, the Wilhelmina Delco Center, one of two Red Cross shelters in the city, had about 200 evacuees. Rain continued to fall steadily in Austin on Sunday, and river levels continued to rise. Precautionary sandbags were stacked against the shelter’s entrance.

Bristel Minsker, communications director for the Red Cross Central and South Texas region, said “things are changing quickly” as the organization prepares to scale up operations in the areas between Austin and Houston.

Houston Mayor Sylvester Turner and other officials pleaded with residents to “shelter in place” and to make calls to overwhelmed 911 operators only in life-threatening emergencies. They urged people to climb to their roofs to await shelter if water was rising in their homes, and local TV news anchors reminded people to stay out of attics where they might be trapped by water – or to take an ax to hack their way to the roof.

The Texas National Guard has deployed across the state, including engineers in Corpus Christi and an infantry search-and-rescue team in Rockport. Another search-and-rescue unit was staging in San Antonio and was likely to be deployed to affected areas shortly, officials said.

As the extent of the disaster became clear at daylight Sunday, some criticized Houston officials for not calling for an evacuation of the city. Turner defended the decision not to evacuate, noting that it would be a “nightmare” to empty out the population of his city and the county all at once.

“You literally cannot put 6.5 million people on the road,” Turner said at a news conference.

Trump praised the way the city’s officials were handling the flood, tweeting at 8:25 a.m. that the “Good news is that we have great talent on the ground.” Trump signed a disaster proclamation for Texas on Friday night after Abbott made a dire request warning that the storm would be deadly and lead to billions in damages.

While Houston had been spared Harvey’s initial onslaught, disaster suddenly beset the city, as severe storms Saturday evening gave way to flooding Sunday morning.

The Weather Service said Sunday that at least five people had been reported dead because of Harvey. Local officials have confirmed that at least three people have died as a result of the storm, and officials in the hardest-hit counties expect that as the waters recede the number of fatalities will rise.

As it scrambled to open shelters across Texas, the Red Cross command center in Houston was “physically isolated” because of floodwaters, said Paul Carden, district director of Red Cross activities in South Texas, which includes Corpus Christi.

“The advice is, if you don’t have to be out, don’t be out,” said Bill Begley, a spokesman with the Joint Information Center in Houston. He said most of the calls for help the center had received had come from residents who tried to drive through the storm and got stuck in high water.

In some cases, people could not wait. Early Monday morning, a man came running into the lobby of the Marriott Courtyard hotel in Southwest Houston. He said he had a pregnant woman in his truck who was about to deliver.

Crystal Manker, the hotel’s operations manager, was shocked enough that anyone made it to the hotel, which had been surrounded by deep, impassable floodwaters and abandoned, submerged cars since the night before. Nobody had gotten in or out for 24 hours. But hotel staff went with the man through the swamped parking lot, and finally into waist-deep water where his truck had stalled, with a pregnant woman and her husband inside.

The man said he had seen the husband’s desperate call on Twitter that his wife was in labor and they couldn’t get out of their home. It was close by, so he and a friend drove through the deep water and picked them up. They started toward Texas Children’s Hospital, but as they got closer to the overflowed Brays Bayou, the water became too deep to pass.

As their truck started stalling, saw the Courtyard, which is on the banks of the Bray, and ran inside to get help. Manker said she called 911, and got through after ten minutes. She told the operator the woman’s contractions were eight minutes apart, and the operator told her to call back when they got closer.

At that point Manker said the baby seemed destined to be born in a hurricane-marooned Marriott, so she and her staff rolled a bed into a ground-floor meeting room. They hurried in with sheets, towels, water, pillows and scissors.

Manker remembered that three nurses from Louisiana had been relocated to the hotel. She called them and they rushed down – even though none of them had ever delivered a baby.

As the mother-to-be lay in the bed in the meeting room for more than an hour, Manker called 911 again and told the operator contractions were down to two minutes apart. The nurses were getting ready.

Then a huge city dump truck appeared. Several men helped the woman into the truck, which then headed off into the 4-foot deep water, across the swamped bridge across the bayou and toward the hospital.

Maker was still waiting for word Monday morning on how everything went. She was most amazed at the men who answered the Twitter call for help.

“They had to be her angel,” she said.

Both of Houston’s major airports were closed, and many tourists and visitors found themselves stranded in hotels with no hope of leaving anytime soon.

Southwest Airlines flight attendant Allison Brown said at least 50 flight attendants, a number of pilots, airport staff members and hundreds of passengers have been stranded at William P. Hobby Airport since at least 1 a.m. Sunday.

Brown said the airport flooded so quickly that shuttles were unable to get them out. They were told by police it would be unsafe to attempt to leave.

“Luckily, we have the restaurant staff, or else we would’ve been stuck with no food,” Brown said. “Waters in the road are around four feet – minimum – surrounding the airport.”

At the Marriott Courtyard Hotel in southwest Houston, along the banks of Brays Bayou, guests woke up to floodwater Sunday morning. In the parking lot, Nichelle Mosby stood with water up to her knees in the parking lot, grimacing with a towel over her head to block the rain.

Mosby and six family members, including a 4-year-old girl, had come from Louisiana to visit relatives. When Harvey hit, they booked into the Courtyard. Now they were stranded with dozens of other guests.

“We went through Katrina, but this feels different,” she said. Instead of a gradual buildup of water, she said, “this was like a gush of water that came up too fast.”

A local television station, KHOU, went offline while covering the rescue of a driver in a semitrailer stuck in more than 10 feet of water near the Interstate 610 loop; the reporter was able to flag down a rescue crew, though the station went dark as the rescue was about to take place.

Hundreds of displaced people have gone to Dallas, about 240 miles north of Houston.

In one, a neighborhood recreation center on the far south side of Dallas, Rebecca Hernandez, 35, said she and her family came from their north Houston home to avoid floodwaters. She, her husband, Gilbert, and their three children drove to Dallas on Friday night. With rent due in a few days, the family couldn’t afford to spend more than one night in a hotel, so they came here.

“We’re starting small,” said Angienetta Johnson, who runs the shelter, noting that there were perhaps 500 or so evacuees in her shelter and another one across town. “But we have plans to go up to 5,000 if need be.”

A neighbor has told Hernandez that floodwaters were at the family’s front door Sunday – just as they were during Katrina.

“We’re ready to go back as soon as they tell us it’s safe,” she said.

Sullivan reported from Houston, Samuels and Berman reported from Washington, and Wax reported from Katy, Texas. The Washington Post’s Fred Barbash, Derek Hawkins, Brian Murphy, Thomas Gibbons-Neff, Susan Hogan, Wesley Lowery and Steven Mufson in Washington; Annie Gowen in New Delhi; Justin Glawe in Dallas; Stephanie Kuzydym and Dylan Baddour in Houston; Tim Craig in Rockport and Corpus Christi; Brittney Martin in San Antonio; Ashley Cusick in New Orleans; Mary Lee Grant in Port Aransas, Texas; and Sofia Sokolove in Austin contributed to this report.