An offshore oil rig has exploded in the Gulf of Mexico, west of the site of the April blast that caused the massive oil spill, coast guards said today.

Coast Guard Petty Officer Casey Ranel said the blast was reported by a helicopter company about 9:30 am local time.

Seven helicopters, two planes and four boats were en route to the site, about 80 miles south of Vermilion Bay along the central Louisiana coast.

Ranel said it was not known whether the structure was a production platform or a drilling rig or whether workers were aboard.

He said smoke was reported but it was unclear whether the rig was still burning.

The Coast Guard said initial reports indicated all 13 crew members from the rig were in the water. One was injured, but there were no deaths.

The platform owned by Mariner Energy is in about 2,500 feet of water and was not currently producing.

About 206 million gallons of oil from an undersea well spilled into the Gulf after BP's Deepwater Horizon rig exploded on April 20, killing 11 workers.