- At least 8 people believed dead as a result of the storm.
- Another 51 centimetres of rain still possible.
- More than 3,000 people rescued so far; 30,000 expected to seek shelter.
- U.S. President Donald Trump to visit Texas on Tuesday.
- Flooding expected to peak Wednesday or Thursday in Houston.
Historic flooding from tropical storm Harvey is believed to have killed at least eight people in Texas and was expected to drive some 30,000 from their homes, as officials on Monday warned that floodwaters would likely rise in the coming days as the storm hovers over the U.S. Gulf Coast.
National Guard troops, police officers, rescue workers and civilians raced in helicopters, boats and special high-water
trucks to rescue the hundreds of people still stranded in and around Houston, the nation's fourth-largest city.
Floodwaters reached the roof lines of single-storey homes Monday and The Associated Press reported people could be heard pleading for help from inside.
The storm was the most powerful hurricane to strike Texas in more than 50 years when it came ashore on Friday near Corpus Christi, 354 kilometres south of Houston.
The National Hurricane Center said Monday night that heavy rainfalls could bring 25 to 50 centimetres of rain overnight.
Death toll expected to rise
Local media put the death toll at eight so far. It is believed to have killed at least six people in Harris County, where Houston is located, according to Tricia Bentley, a spokeswoman for the county coroner's office, including a man who died in a house fire and an elderly woman attempting to drive through flooded streets on the city's west side.
The number also includes a 60-year-old woman who died in neighbouring Montgomery County when a tree fell on her trailer home while she slept, according to the local medical examiner.
Police Chief Art Acevedo said he's "really worried about how many bodies we're going to find."
As stunned families surveyed the wreckage of destroyed homes and roads flooded or clogged with debris, Texas Gov. Greg Abbott warned Houstonians to brace for a long recovery.
"We need to recognize this is going to be a new and different normal for this entire region," Abbott told reporters after touring Corpus Christi.
Harvey was expected to linger over Texas's Gulf Coast for the next few days, with threats of flooding extending into Louisiana.
The storm was generating an amount of rain that would normally be seen only once in more than 1,000 years, said Edmond Russo, a deputy district engineer for the U.S. Army Corps of Engineers.
In scenes evoking the aftermath of Hurricane Katrina in New Orleans in 2005, police and coast guard teams have rescued at least 3,000 people so far, plucking many from rooftops by helicopter, as they urged the hundreds believed to be marooned in flooded houses to hang towels or sheets outside to alert rescuers.
Harvey's centre was 137 kilometres south-southwest of Houston on Monday afternoon and forecast to arc slowly toward the city through Wednesday, with the worst floods expected later that day and on Thursday.
Schools and office buildings were closed throughout the metropolitan area, home to 6.8 million people, as chest-high water filled some neighbourhoods in the low-lying city.
Numerous refiners shut operations in the nation's refining and petrochemical hub.
The city's normally bustling business district was virtually deserted, with emergency vehicles making up most of the traffic. Most traffic signals were out and most businesses closed.
The U.S. Army Corps of Engineers said Monday that it was releasing water from the nearby Addicks and Barker reservoirs into Buffalo Bayou, the primary body of water running through Houston.
"The more they release it could go up and it could create even additional problems," Houston Mayor Sylvester Turner warned. But the release was said to be necessary to prevent an uncontrolled surge of water, which Turner said "would be exponentially worse."
Citizens to the rescue
Torrential rain also hit areas more than 240 kilometres away, swelling rivers upstream and causing a surge that was heading toward the Houston area, where numerous rivers and streams already have been breached.
The high floodwaters made it hard for some residents who had fled their homes to find shelter. Christe Fletcher, 37, fled her house after it flooded to waist-deep, but was struggling to find a safe route to a nearby hotel.
"It's kind of hard to get there because all of the roads are closed," she said. "It's the worst experience you can go through."
Chris Thorn drove with a buddy from the Dallas area with their flat-bottom hunting boat to pull strangers out of the water.
"I couldn't sit at home and watch it on TV and do nothing since I have a boat and all the tools to help," he said.
'I don't even have flood insurance'
They got to Spring, Texas, where Cypress Creek had breached Interstate 45 and went to work, helping people out of a gated community near the creek.
"It's never flooded here," resident Lane Cross said from the front of Thorn's boat, holding his dog, Max. "I don't even have flood insurance."
By Monday night, 7,000 people had arrived at a shelter set up inside the George R. Brown Convention Center — which originally had an estimated capacity of 5,000.
Red Cross spokesman Lloyd Ziel said that volunteers made more space inside the centre, which also was used to house Hurricane Katrina refugees from New Orleans in 2005, in part by pushing some cots closer together. A shortage of cots means some people will have to sleep on chairs or the floor
Many area residents were left in limbo, wondering what remained of their flooded homes.
'I'm not complaining, we're alive'
Regina Costilla, 48, said she and her 16-year-old son had been rescued from their home by a good Samaritan with a boat. She sat and worried until she was reunited with her husband and large dog, who had been left behind because they didn't fit into the boat.
"I'm not complaining, we're alive," said Costilla. "When I saw the forecast of the storm I said I'll be happy if we get out
with our lives."
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Houston did not order an evacuation due to concerns about people being stranded on city highways now consumed by floods, Turner said.
FEMA's Long on Monday did not question the decision, saying the "evacuation of the city of Houston could take days, days, literally days."
Gov. Abbott, who had suggested on Friday that people leave the area, declined to second-guess the mayor on Monday, telling reporters, "Decisions about evacuations are something that are behind us."
Trump to visit
U.S. President Donald Trump plans to go to Texas on Tuesday to survey the damage, a White House spokesperson said on Sunday. On Monday, he approved an emergency declaration for Louisiana.
Trump, facing the biggest U.S. natural disaster since he took office in January, signed a disaster proclamation for Texas on Friday, triggering federal relief efforts.
"We're dealing with Congress. As you know it's going to be a very expensive situation," Trump told reporters on Monday.
Trump's administration assured Congress that the $3 billion US balance in FEMA's disaster fund was enough to handle immediate needs, such as debris removal and temporary shelter for thousands of displaced residents. When lawmakers return next week, a multibillion-dollar aid package is likely to be added to their already packed agenda.