Media playback is unsupported on your device Media caption Amateur footage shows the chemical plant ablaze

At least one person has been killed and another 70 injured in an explosion and fire that tore through a chemical plant in the US state of Louisiana.

The blast happened at the Williams Olefins chemical plant in Geismar, south of Baton Rouge, at about 08:30 local time (13:30 GMT), officials said.

Nearby residents have been told to stay indoors with their windows closed.

The plant produces flammable gases used in the petrochemical industry. The cause of the blast is unclear.

Louisiana State Police Capt Doug Cain said a body was recovered at the scene by a hazmat (hazardous materials) team and a search was continuing for more victims.

Police later named the man killed as Zachary C Green, 29, of Hammond, Louisiana.

Louisiana's health department said that 73 people had been treated at hospitals for injuries ranging from minor to critical.

Eight of the injured were taken to Baton Rouge Medical Center where one was listed in critical condition and two others were in serious condition.

Tests have not found dangerous levels of chemicals in the air so far, officials said.

Footage from the scene showed a huge pall of black smoke over the plant. Major roads around the site have been sealed off.

Witness Daniel Cuthbertson, a fuel lorry operator, said the explosion shook the ground and was followed by a "ball of fire".

Image caption Aerial pictures after the fire was out showed the extent of the damage

He said workers climbed over gates in their scramble to escape the scene.

State police said that by the afternoon all of the plant's more than 300 workers had been accounted for.

A statement from Williams said that emergency shut-down valves had been closed at the plant and the unit was isolated.

"Our emergency-response crews are thoroughly trained to respond to these types of incidents and are diligently performing their work with their first priority being the safety and well-being of people in and around the area," the statement said.

"We are in the process of accounting for all personnel."

In April at least 15 people were killed and scores injured by an explosion at a fertiliser plant near Waco in the state of Texas.