An offshore drilling platform caught fire and a fuel tank aboard exploded Saturday, and authorities said they would just have to let the blaze burn itself out. There were no injuries.

The initial fire broke out about 4:15 a.m., said Coast Guard Petty Officer Elizabeth Brannan. Then, about four hours later, a fuel tank on board the platform exploded, forcing two groups of firefighters off the deck.The firefighters were not hurt, and neither were the two workers on the platform at the time the original fire broke out, she said. There was no evidence any of the fuel spilled into the ocean, she said.

The platform, about two miles off the Gloucester coast north of Boston, is used to drill pipelines to dispose of sewage at sea.

After the explosion, Coast Guardsmen and firefighters tried battling the blaze from the water before deciding to let it burn out, Brannan said. Rainstorms were helping dampen the fire, she said.

"Basically they're just standing off and waiting for the fire to go out on its own," Brannan said.

There are several other fuel tanks on the platform, in addition to the one that exploded. But Brannan said there was believed to be little chance any other of the tanks would explode.

The cause of the fire was not immediately known.

The owners of the platform, Maitland Brothers of Louisiana, told authorities they would assume responsibility for the fire, and have hired Clean Harbors Inc., a company involved in the cleanup of Boston Harbor, Brannan said.

Phone calls placed to Maitland Brothers went unanswered Saturday afternoon.

Four Coast Guard cutters, a fireboat from the Massachusetts Port Authority and several smaller boats - all equipped with fire-fighting equipment - were called to fight the blaze. A helicopter also was dispatched to the site.