“Catastrophic” flooding in the United States 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 said that number could nearly double later this week. 

President Donald Trump will visit Texas today to survey the damage, a White House spokeswoman said. He approved an emergency declaration for Louisiana yesterday. Trump, facing the biggest U.S. natural disaster since he took office in January, signed a disaster proclamation for Texas on Friday, triggering federal relief efforts.

Almost half of the U.S. refining capacity is in the Gulf region. Shutdowns extended across the coast, including Exxon Mobil’s facility in Baytown, the nation’s second largest refinery. About 13 percent of daily U.S. capacity was offline as of Monday morning.

The outages will limit the availability of U.S. gasoline and other refined products and push prices higher, analysts said. Gasoline futures rose as much as 7 percent yesterday. Damages are not likely to be as extensive as Katrina, which killed 1,800 people in and around New Orleans, or Sandy, which hit New York in 2012, said a spokeswoman for Hannover Re, one of the world’s largest reinsurers. Those caused $80 billion and $36 billion in insured losses, respectively.

Some 30,000 residents of the nation’s fourth-largest city were expected to be left temporarily homeless by Harvey, which became the most powerful hurricane to strike Texas in more than 50 years when it came ashore on Friday near Corpus Christi, about 220 miles (354 km) south of Houston.

Stunned families surveyed the wreckage of destroyed homes along the nearby coast and roads that were not flooded were clogged with debris. Death estimates vary, but at least two people have been confirmed killed by the storm. About 5,500 people were in shelters as of yesterday morning, city officials said.

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Many area residents were left in limbo, wondering what remained of their flooded homes. 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.  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.

“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.

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.