“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.
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.
Up to 2,000 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.
The area is expected to have received a year's rainfall within a week. Five people are reported dead. Helicopters have plucked victims from rooftops.
Officials say 30,000 people are expected 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”.
The National Weather Service 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.
An inundated care home in Dickinson, about 30 miles (50 km) south east of the city, has now been evacuated by helicopter after an image of several elderly women sitting in a lounge in waist-deep water went viral on social media.
Similar levels of 15-25in of rain are predicted for south-western and central Louisiana.
The state saw huge destruction following Hurricane Katrina in 2005.
Observers have drawn comparisons with the disastrous evacuation of homes in New Orleans ahead of Katrina, which left thousands of people stranded in squalid conditions at that city's stadium.
Tens of thousands of people have been ordered to leave parts of Fort Bend County, about 35 miles south-west of Houston, where a river is set to crest this week.
But Houston authorities have not issued a mass evacuation order.
Mayor Sylvester Turner on Sunday defended the decision by citing the “crazy” logistics of planning an evacuation of 2.3 million people.
Meanwhile, Dallas, 240 miles north of Houston, will set up a “mega shelter” at its convention centre to house 5,000 evacuees, city officials said.
