Tropical Storm Harvey has unleashed catastrophic flooding in Houston, the largest city in the US state of Texas, turning streets into raging rivers, as trapped residents climbed to higher floors and authorities reported several deaths.

One of the fatalities, a man, was killed when a fire hit a Houston-area home during the storm, while a woman drowned as she tried to get out of her vehicle in high water, the Texas Tribune reported on Sunday.

Local news outlet, Houston Chronicle, quoted the National Weather Service as saying that five people had died so far, while the death toll was expected to rise.

City officials received at least 2,000 emergency calls from residents as waters continue to rise, leaving thousands of homes flooded and motorists stranded. More than 1,000 residents were rescued from flash floods overnight, authorities said.

"It is bad and growing worse," said Texas Governor Greg Abbott, who added that the Category 4 storm, which first crashed ashore on the Gulf Coast on Friday, had inflicted billions of dollars in damage.

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"This appears to be either the worst or one of the worst floods Houston has ever had. We are measuring it not in inches but in feet," Abbott told CBS television news.

This event is unprecedented & all impacts are unknown & beyond anything experienced. Follow orders from officials to ensure safety. #Harvey pic.twitter.com/IjpWLey1h8 — NWS (@NWS) August 27, 2017

"This event is unprecedented and all impacts are unknown & beyond anything experienced," the National Weather Service said on Twitter.

US President Donald Trump, who was spending the weekend at the Camp David presidential retreat, said "the focus must be on life and safety" in responding to the disaster.

The White House later announced on Sunday that the president will be visiting Texas on Tuesday.

Houston began opening community centres to shelter people forced out of their homes, but House Mayor Sylvester Turner appealed to residents to stay put and not call the 911 emergency line unless they faced a life-threatening situation.

"Do not get on the road. Even if there's a lull today, don't assume the storm is over," Turner said at a news conference on Sunday. "The best way to keep from being stranded is to stay off the streets."

He defended his decision not to order a mass evacuation before the storm, saying moving 2.3 million people would only create a "nightmare".

Houston's Bush Intercontinental Airport cancelled all commercial flights on Sunday after flooding inundated access roads.



The city's only other airport, Hobby International, had earlier stopped all flights "due to standing water in runways".

Fast-growing metropolis

The US weather service said about 60cm of rain fell in Houston and nearby Galveston in a 24-hour period.

"If the highest floor of your home becomes dangerous ... get on the roof!" Houston's emergency management agency warned in a bulletin.

Images captured by Al Jazeera showed rescue boats and rafts carrying several people while navigating the city's flooded streets.

Another photo that became viral on social media showed elderly women, trapped in floodwaters in a nursing home in Galveston, southeast of Houston and adjacent to the Gulf of Mexico.

Al Jazeera's Heidi Zhou-Castro, reporting from Houston, said as of 17:00 GMT on Sunday, water is expected to rise further with rainfall predicted in the next two days or more.

Harvey was the most powerful storm to hit the US mainland since 2005.

It slowly weakened as it advanced inland, but it had the power to rip off roofs, flip mobile homes and leave hundreds of thousands of people in the dark on the Gulf Coast, home to some of the country's most important oil refineries.

More than a dozen tornado warnings were issued overnight for southeast Texas, including several in the Houston area.

Search and rescue operations were also under way in devastated coastal communities including Corpus Christi, a city of some 325,000 people, Governor Abbott said.

William Long, the US emergency chief, described Harvey a "devastating disaster".

Coastal Texas is a fast-growing area, with some 1.5 million people moving into the region since 1999. It is also home to a large number of oil refineries and a number of major ports.

US authorities said about 22 percent of crude production in the Gulf of Mexico, accounting for more than 375,000 barrels a day, was shut down as of Friday.