An explosion ripped through an oil rig in the Gulf of Mexico yesterday, dumping 13 people into the water, one of whom was injured, the US Coast Guard said.

''All 13 are accounted for and they are all wearing some sort of an immersion suit that protects them from the water,'' Coast Guard chief petty officer John Edwards told MSNBC.

Nine helicopters had been dispatched to the rig 130km south of Vermilion Bay in Louisiana, the spokesman said, adding the extent of any injuries suffered by the workers was not immediately clear.

Four Coast Guard cutters were also en route to the rig, said to be owned by Mariner Energy, and which was reportedly still ablaze. "Right now we're focused on search and rescue and then, ultimately, as this thing progresses, we're going to be looking into the cause," Edwards added.

The blast comes four months after an explosion ripped through the BP-leased Deepwater Horizon rig, some 80km off Louisiana, killing 11 workers and unleashing an environmental catastrophe.