The Coast Guard says no one was killed in the blast, which was reported by a commercial helicopter flying over the area Thursday morning. All 13 people aboard the rig have been accounted for, with one injury. The extent of the injury was not known.

Coast Guard Cmdr. Cheri Ben-Iesau said some of those from the rig were spotted in emergency flotation devices.

Seven Coast Guard helicopters, two airplanes and three cutters were dispatched to the scene from New Orleans, Houston and Mobile, Ala., Ben-Iesau said. She said authorities do not know whether oil was leaking from the site.

The Department of Homeland Security said the platform was in about 2,500 feet of water and owned by Mariner Energy of Houston. DHS said it was not producing oil and gas.

The Deepwater Horizon rig leased by BP was in about 5,000 feet of water when it exploded and sank in April, killing 11 workers and triggering a leak of about 206 million gallons of oil.