Large parts of Texas were under a flash flood warning on Monday after a storm system dumped almost half a metre rain in areas near Houston, causing hundreds of cancelled flights, closed roads and massive power outages.

One death has been reported, Channel 13 in Houston said, from storms that have caused nearly 900 water rescues in the country's fourth-largest city.

The National Weather Service also issued a flash flood watch extending through much of central Texas, into western Louisiana and Arkansas.

Ed Emmett, the top political official for Harris County, signed a disaster declaration for the county that contains Houston after more than 1,000 homes flooded there.

Emmett told a news conference that 13 creeks and water channels designed for drainage had overflowed, causing floods that blocked roads to downtown and other parts of the city. Floods have also hit highways running through Houston, including Interstate 10, a major U.S. east-west corridor.

Many without power

In Houston, more than 70 residential subdivisions reported flooding and Mayor Sylvester Turner cancelled his State of the City speech planned for Monday, instructing all non-essential city employees to stay home.

"This not the day to be on the roads in the city of Houston," Turner told reporters.

The city has turned one shopping mall into an evacuation center.

More than 70,000 customers were without power in the Houston area on Monday morning due to the severe weather, CenterPoint Energy reported as it worked to fix outages.

The rains were expected to cause rivers to crest later in the week, bringing floods to downstream areas, the weather service said.

In the San Antonio and Austin areas, torrential rains have closed streets, caused traffic accidents and led to dozens of people being rescued from cars stuck in high water.

© Thomson Reuters, 2016