Explosions and fires cause 'dangerous' plume of smoke at Houston chemical plant flooded by Harvey rain

Two explosions ripped through a flooded chemical plant in hurricane-ravaged Houston, sparking fires which are sending up plumes of "incredibly dangerous" smoke, authorities have said.

The blasts at the Arkema plant, around 25m (40km) north-east of the Texan city, send flames shooting up to 40ft in the air - and the French operator of the plant warned that up to eight more chemical containers could explode.

The explosions happened as officials struggle to tackle devastation left in the wake of Hurricane Harvey, as several days of unrelenting rain finally began to recede.

ABC13 reporter Courtney Fisher, who filmed fire trucks near the scene, said more than a dozen had been sent to the plant as officials confirmed explosions and black smoke.

Fire chiefs said the blasts were small and while some deputies had suffered irritated eyes from the smoke, they said the materials which caught fire were not toxic.

However, at a conference in Washington DC, Brock Long - administrator of the Federal Emergency Management Agency - told reporters that the plume of smoke spotted over the plant was hazardous.

The Texas Commission on Environmental Quality also urged people in the area to stay indoors with their windows closed and air conditioners running, and to limit any physical activity.

The site was shut before Harvey made landfall last week, while all remaining staff were sent home on Tuesday.

Homes within a 1.5-mile radius of the plant have been evacuated, though officials said it was not mandatory.

Homes within a 1.5-mile radius of the plant have been evacuated. Credit: AP

Five days of torrential rain has submerged Houston, America's fourth-largest city, while three flood defences - one of which is designed to withstand a "1,000-year flood" - have overflown.

An explosion and intense fire had been expected as the plant is surrounded by six feet of water, meaning chemical compounds - which must be stored at low temperatures - will warm up.

Bob Royall, Assistant Chief Harris County Fire Marshal Office, confirmed there was a series of small explosions after a "chemical decomposition" in a box van created a chemical reaction on the site of the plant in Crosby.

He warned eight more containers of a similar type on the plant site could also burn and explode but said what had happened was "exactly what we expected was going to happen".

Officials are struggling to cope in the aftermath of Hurricane Harvey Credit: AP

He said: "Now I don't want the public to think that these are massive explosions.

"We're trying to make sure that our citizens are comfortable with what's going on and they know the truth and with that these are small container ruptures that may have a sound of a pop or something of that nature - this is not a massive explosion."

Meanwhile, US President Donald Trump has promised billions of pounds in aid to help Texas rebuild.

It is believed that the US has $2.3 billion in disaster funds.

Harvey was downgraded to a tropical depression on Thursday, but experts expect more catastrophic flooding.

People in Houston take shelter inside a hall. Credit: AP

The death toll from Harvey has been raised to more than 30 but could still rise.

Police said officers had found a submerged van in which a Houston family of six was killed as they tried to escape the flood waters.

The two grandparents and four children, aged six to 16, died after their van sank in Houston.

Around 24,000 members of the National Guard are being deployed in the state to help with disaster relief.

Houston's mayor, Sylvester Turner, imposed a night-time curfew between 10pm and 5am in a bid to prevent looting and protect public safety.