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

A second person has died from an explosion that tore through a chemical plant in the US state of Louisiana.

Scott Thrower, 47, died from his injuries at a hospital burn centre. Another worker, Zachary Green, 29, died on Thursday; 100 people were injured.

Meanwhile, US officials have launched an investigation into the blast, though the FBI has ruled out terrorism.

The explosion occurred on Thursday morning at the Williams Olefins plant in Geismar, south of Baton Rouge.

Five people remained in hospital in conditions ranging from critical to fair on Friday.

'Too early'

The plant produces flammable gases used in the petrochemical industry.

Tests have not found dangerous levels of chemicals in the air so far, officials said, but nearby residents were told to stay indoors with their windows closed on Thursday.

A company investigation will begin when the plant is safe to re-enter, plant manager Larry Bayer said.

The extent of the damage is still unknown, Mr Bayer said. A small number of employees were working in 12-hour shifts "to assure the plant is being safely shut down and monitored," he added.

The US Occupational Safety and Health Administration is also investigating the cause of the blast, but a spokesman said it was "too early to determine anything".

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

'Ball of fire'

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

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

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

The firm said 839 people were working inside the plant at the time of the explosion. It was a larger-than-normal workforce because a major expansion was under way.

Both men who died in the blast had worked at Williams Olefins.

On Thursday, Louisiana Governor Bobby Jindal vowed to hold responsible whoever was at fault.

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