Houston floods: ‘Catastrophic’ flooding from Harvey to worsen

US President Donald Trump has promised swift action to help those affected. He is due to visit Texas on Tuesday.

“Recovery will be a long and difficult road and the federal government stands ready, willing and able to support that effort,” he said.

He said he was dealing with Congress on funding, warning “it’s going to be a very expensive situation”.

Mr Trump has also approved an emergency declaration for neighbouring Louisiana.

Harvey made landfall as a category-four hurricane late on Friday, bringing flooding described by officials as unprecedented. It was later downgraded to a tropical storm.

More than 3,000 people have been rescued in and around Houston, the fourth-largest city in the US, where about 6.6m people live in the metropolitan area. Helicopters have plucked victims from rooftops.

At least nine people are reported to have died in incidents related to the storm, Texan officials say.

Six members of the same family died trying to flee rising floodwaters, relatives told US media, but the incident has not been confirmed.

Governor Greg Abbott has activated the entire Texas National Guard – some 12,000 so-called “civilian soldiers” – to assist national forces in search and rescue operations.

The area is expected to have received a year’s rainfall within a week.

Officials expect half a million disaster victims to seek assistance in Texas and 30,000 people to be housed in emergency shelters.

“Catastrophic and life-threatening flooding will continue across south-eastern Texas,” the National Hurricane Center said on Monday.

“Additional rainfall accumulations of 15 to 25 inches are expected”.

Meanwhile, army engineers have begun releasing water from two dams controlling water flowing along a major river into the heart of Houston.

Officials said they were opening the Addicks and Barker dams to stop water spilling into neighbouring communities, but that this could cause further damage down the Buffalo Bayou.

The National Weather Service (NWS) said the worst of floods were expected on Wednesday and Thursday, Reuters reports, although there is still uncertainty about the storm’s path.

Thousands of homes are without electricity.

• The massive economic cost of the flood

Many schools are closed – as are Houston’s two main airports, with runways completely flooded.

The Texas Gulf Coast is a key centre of the US oil and gas industry, and some of the largest refineries in the country have halted operations.