“Catastrophic” flooding in the US state of Texas is only expected to worsen in coming days as waters rise following a storm of historic proportions.
A record 30in of rain (75cm) has already fallen on the city of Houston in the wake of Hurricane Harvey, turning roads into rivers.
But forecasters say that number could nearly double later this week.
On Monday President Donald Trump also approved an emergency declaration for neighbouring Louisiana.
“They’re saying it’s the biggest. It’s a historic amount of water, there’s never been anything like it,” he told reporters.
He paid tribute to rescue teams and the “spirit” of people in Texas, saying he was dealing with Congress on funding as he prepared to visit the state on Tuesday.
“It’s going to be a very expensive situation,” he said.
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.
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. (Courtesy BBC)