Explosions have been reported at a chemical plant near the flooded US city of Houston.

Explosions have been reported at a chemical plant near the flooded US city of Houston.

US media report witnesses as hearing two blasts and seeing black smoke issuing from the Arkema plant at Crosby.

During heavy rainfall from Hurricane Harvey, the complex lost the ability to refrigerate chemical compounds that need to be kept cool.

There was no way to prevent an explosion, the company warned earlier.

At least 33 people have been killed in the aftermath of the storm, which the US National Weather Service has now downgraded to a tropical depression.

Heavy rainfall is expected from Louisiana to Kentucky over the next three days, and flood warnings remain in effect for south-east Texas and parts of south-west Louisiana.

US energy supplies have been hit, as oil companies shut down refineries and a major pipeline in the Houston area.

Firefighters will begin a door-to-door search of badly flooded areas of Houston on Thursday, to rescue survivors who are still stranded and recover the bodies of those who have died.

"We'll be doing block-by-block, door-by-door search of streets... to make sure there are no people we've left behind," Richard Mann, the city's assistant fire chief, was quoted as saying by the Houston Chronicle newspaper.

"This will be a one- to two-week-long process to make sure we address all those areas that have been... most impacted."

What happened at the chemical plant?

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The Arkema chemical plant, 21 miles (34km) from Houston, shut down its production on Friday, before the storm made landfall.

But 40in (102cm) of rainfall in the area flooded the site and cut off its power, the company said in a statement. Back-up generators were also flooded.

The facility manufactures organic peroxides, compounds that are used in everything from making pharmaceuticals to construction materials, which can become dangerous at higher temperatures.

"Any fire will probably resemble a large gasoline fire," CEO Richard Rowe told Reuters news agency before the reports of explosions. "The fire will be explosive and intense."

He said the black smoke produced would irritate skin, eyes and lungs.

"The high water that exists on site, and the lack of power, leave us with no way to prevent it."