A petrol barge being unloaded in a US oil depot exploded with a thunderous blast yesterday, killing at least one worker and sending a fiery column of black smoke so high it could be seen more than 30 miles away.

With the US on high alert for terrorism, the explosion and raging fire in New York harbour about 20 miles from the World Trade Centre attacks unnerved New York and New Jersey residents, but authorities said there was no indication terrorists were involved.

One worker was killed, another was unaccounted for, and an employee of Exxon Mobil Corporation, the owner of the depot, was in a critical condition with third-degree burns, officials said.

The cause of the blast was under investigation.

"I looked up at the sky, and I saw pieces of metal flying all over," said worker Jaime Villa, who was repairing a pump when the barge blew up.

"I ran as fast as I could go. I was so scared that I lost my breath and I fell to the ground."

The barge, which contained about four million gallons of unleaded petrol, was being unloaded at the 200-acre petroleum storage facility when the explosion occurred, said Prem Nair, an Exxon Mobil spokeswoman. About half of the cargo had been unloaded.

The barge eventually sank. The fire took about three hours to contain.

The company would not speculate on a cause of the explosion.