HOUSTON (CBSNewYork/CBS News/AP) — The remnants of Tropical Storm Harvey sent devastating floods pouring into Houston Sunday, as rising water chased thousands of people to rooftops or higher ground and overwhelmed rescuers who could not keep up with the constant calls for help.

The incessant rain covered much of Houston in turbid, gray-green water and turned streets into rivers navigable only by boat. In a rescue effort that recalled the aftermath of Hurricane Katrina, helicopters landed near flooded freeways, airboats buzzed across submerged neighborhoods and high-water vehicles plowed through water-logged intersections. Some people managed with kayaks or canoes or swam.

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PHOTOS: Southeast Texas Devastated By Harvey Floodwaters

Kristine Johnson reported for CBS News that the National Hurricane Center southern Texas was experiencing “catastrophic flooding” from Hurricane Harvey through the day Sunday. At least 24 inches of rain have been dumped onto the region in just 24 hours, and much more is expected before the week is through.

Judging from federal disaster declarations, the storm has so far affected about a quarter of the Texas population, or 6.8 million people in 18 counties. It was blamed for at least two deaths.

“This is a historical weather event for the region and it is expected to last for the next few days,” said Kevin Oditt, Commanding Officer of Coast Guard Sector Houston-Galveston.

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Storm surges of up to 12 feet were also anticipated.

On Sunday morning, Harvey was a tropical storm with maximum sustained winds of 45 mph. The storm made landfall late Friday as a powerful Category 4 hurricane.

Hurricane Harvey Brings Major Floods To Houston Area

At least two people were people were dead and many more were injured as a result of the hurricane as of Sunday evening.

One person was killed in Aransas County when in a fire at home during the storm, county Judge C.H. “Burt” Mills Jr. said.

Another person — a woman who tried to get out of her vehicle in high water — died in flooding in Harris County, where Houston is located, though authorities had not confirmed a cause of death, said Gary Norman, a spokesman for the Houston emergency operations center.

As many as 14 people suffered minor injuries, including slips and falls, scrapes and a broken leg, Mills said.

About 300,000 customers were left without power statewide. Gov. Greg Abbott said it would probably be several days before electricity is restored.

Six counties have been declared federal disaster areas.

In the midst of the disaster Sunday, helicopters, boats and high-water vehicles swarmed around inundated Houston neighborhoods, pulling people from their homes or from the turbid water, which was high enough in some places to gush into second floors.

The flooding was so widespread that authorities had trouble pinpointing the worst areas. They urged people to get on top of their homes to avoid becoming trapped in attics and to wave sheets or towels to draw attention to their location.

As the water rose, the National Weather Service offered another ominous forecast: Before the storm passes, some parts of Houston and its suburbs could receive as much as 50 inches of rain. That would be the highest amount ever recorded in Texas.

“The breadth and intensity of this rainfall is beyond anything experienced before,” the National Weather Service said in a statement.

Average rainfall totals will end up around 40 inches for Houston, weather service meteorologist Patrick Burke said.

The director of the Federal Emergency Management Agency, Brock Long, said the government expected to conduct a “mass care mission” and predicted that the aftermath of the storm would require FEMA’s involvement for years.

“This disaster’s going to be a landmark event,” Long said.

Rescuers had to give top priority to life-and-death situations, leaving many displaced families to fend for themselves. The city’s main convention center was quickly opened as a shelter.

Gillis Leho arrived there soaking wet. She said she awoke Sunday to find her downstairs flooded. She tried to move some belongings upstairs, then grabbed her grandchildren.

“When they told us the current was getting high, we had to bust a window to get out,” Leho said.

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Harris County Sheriff Ed Gonzalez used Twitter to field calls for assistance. Among those seeking help was a woman who posted: “I have 2 children with me and the water is swallowing us up.”

Some people used inflatable beach toys, rubber rafts and even air mattresses to get through the water to safety. Others waded while carrying trash bags stuffed with their belongings and small animals in pet carriers.

Houston Mayor Sylvester Turner said authorities had received more than 2,000 calls for help, with more coming in. He urged drivers to stay off flooded roads to avoid adding to the number of those stranded.

“I don’t need to tell anyone this is a very, very serious and unprecedented storm,” Turner told a news conference. “We have several hundred structural flooding reports. We expect that number to rise pretty dramatically.”

The mayor defended his decision not to ask residents to evacuate before the heavy rain from Harvey swamped roads and neighborhoods. He said there was no way to know which areas were most vulnerable.

“If you think the situation right now is bad, and you give an order to evacuate, you are creating a nightmare,” he said, citing the risks of sending the city’s 2.3 million inhabitants onto the highways at the same time.

Rainfall of more than 4 inches per hour resulted in water levels higher than in any recent floods and higher than during Tropical Storm Allison in June 2001, said Jeff Linder of flood control district in Harris County, which includes Houston.

Rescuers came by land, water and air.

On Interstate 45 south of downtown, television video showed people climbing over concrete dividers to get to a high-wheel dump truck that appeared to be wheels-deep in water on a service road. They clambered up the side of the truck to get into the dump box.

In Friendswood near Houston, authorities asked people with flat-bottomed airboats or fuel for them to help rescue people.

Jesse Gonzalez, and his son, also named Jesse, used their boat to rescue people from a southeast Houston neighborhood. Asked what he had seen, the younger Gonzalez replied: “A lot of people walking and a lot of dogs swimming.”

“It’s chest- to shoulder-deep out there in certain areas,” he told television station KTRK as the pair grabbed a gasoline can to refill their boat.

The Coast Guard, which received more than 300 requests for help, deployed five helicopters and asked for additional aircraft from New Orleans.

Staff at Houston CBS affiliate KHOU-TV were broadcasting live coverage of the floods when they had to evacuate after water started to gush into the building. The anchors and news operations at KHOU moved first to a second floor before finally abandoning the station.

Rainfall totals climbed by the hour. Since Thursday, South Houston had received nearly 25 inches and the suburbs of Santa Fe and Dayton got 27 inches.

In the island community of Port Aransas, population 3,800, officials were unable to fully survey the town because of “massive” damage. Police and heavy equipment had only made it into the northernmost street.

“I can tell you I have a very bad feeling and that’s about it,” said Mayor Charles Bujan, who had called for a mandatory evacuation but did not know how many heeded the order.

Some of the worst damage appeared to be in Rockport, a coastal city of about 10,000 that was directly in the storm’s path. The mayor said his community took a blow “right on the nose” that left “widespread devastation,” including homes, businesses and schools that were heavily damaged. Some structures were destroyed.

Rockport’s roads were a mess of toppled power poles. A trailer blocked much of one major intersection. Wood framing from ripped-apart houses was strewn along Route 35 on the town’s southern end.

Harvey’s relentless wind tore the metal sides off the high school gym and twisted the steel door frame of its auditorium.

“We’re still in the very infancy stage of getting this recovery started,” said Aransas County spokesman Larry Sinclair.

President Trump will travel to Texas on Tuesday to review the state’s recovery efforts, according to White House Press Secretary Sarah Huckabee Sanders.

“We are coordinating logistics with state and local officials, and one details are finalized we will let you know,” Sanders said in a statement to CBS News Sunday afternoon. “We continue to keep all of those affected in our thoughts and prayers.

Meanwhile, New York City has sent 120 emergency personnel to Texas to assist in the aftermath the storm, Mayor Bill de Blasio announced early Sunday. A Red Cross team from New York was also headed to Texas on Sunday.

The flooding is expected to continue through the day and likely the night.

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