Woman stands on her front door as she surveys her property devastated by Hurricane Harvey in Rockport, Texas
Petrol prices jumped to two-year highs as Houston is in the grip of the biggest storm in the history of the state of TexasREUTERS/Adrees Latif

Petrol prices jumped to two-year highs as Tropical Storm Harvey wreaked havoc along the US Gulf coast.

US prices for petrol for delivery in September surged as high as 7% to $1.7799 per gallon, the highest level since late July 2015, as ten oil refineries were forced to shut down as a result of the storm in the Houston and Corpus Christi areas.

The region is one of the country's key energy hubs, with the closed refineries having the capacity to process about 2 million barrels of oil a day.

Overall, the Gulf area is home to refineries and other operations that account for nearly one-third of the nation's capacity to turn oil into gas, diesel and other products.

"Gasoline prices are going to continue to rise this week as we expect another three days of rain in the Houston area," Andy Lipow, president of consultant Lipow Oil Associates LLC in Houston, told Bloomberg News.

Meanwhile, Houston – America's fourth-biggest city – is in the grip of the biggest storm in the history of the state of Texas, officials say.

Two people are confirmed to have died so far – including a woman who tried to get out of her car in high water in Harris County - although the Houston Chronicle was reporting that six people had died.

Texas Governor Greg Abbott said conditions were "bad and growing worse" as National Guard troops were deployed to the city overnight.

Up to 2,000 people have been rescued in and around Houston, with about 6.6 million people living in the metropolitan area.

Once-in-500-year flooding

Waters have reached as high as second-storey homes as the deluge from storm Harvey dumps tens of inches of rain on the state.

The US National Weather Service says conditions are "unprecedented". A "flash flood emergency" is in force across the Houston area, with travel near impossible.

Thousands of homes are without electricity. Many schools are closed – as are the two main airports, with runways completely flooded.

Houston Mayor Sylvester Turner told residents: "Don't get on the road. Don't assume this storm is over."

Houston's main public hospital ­– Ben Taub – is to be evacuated after a busted sewer pipe forced officials to close the kitchen, but the evacuation cannot begin because the building is surrounded by waist-deep water.

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.

President Trump said "major rescue operations" are under way, and tweeted: "Wow - Now experts are calling #Harvey a once in 500 year flood! We have an all out effort going, and going well!"

Insurance experts quoted by Reuters news agency say it could equal the devastation inflicted by Hurricane Katrina in 2005 - reportedly the most expensive natural disaster in US history.

Katrina caused about $15bn (£11.6bn) of flood damage in the states of Louisiana and Mississippi.