UPDATE 6-US Gulf gas explosion injures six, one missing

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HOUSTON, March 12 (Reuters) - A natural gas explosion injured six crew members of a pipeline maintenance vessel off the coast of Louisiana and left one person missing, the U.S. Coast Guard said on Wednesday.

The explosion occurred late Tuesday while the Motor Vessel Jillian Morrison was clearing the gas from a shut section of a pipeline owned by ANR Pipeline Co into a tank towed behind the vessel, said Petty Officer James Harless, a Coast Guard spokesman.

The towed tank ruptured in the explosion, Harless said. Coast Guard investigators checked the pipeline and wellhead for damage at the location of the explosion 15 miles (24 km) off the coast of Marsh Island, Louisiana.

ANR's parent company, TransCanada Corp (TRP.TO: Quote, Profile, Research, Stock Buzz), said the blast did not affect its pipeline system or supplies of natural gas to customers.

El Paso Corp's (EP.N: Quote, Profile, Research, Stock Buzz) Tennessee natural gas pipeline, however, said the explosion led it to declare force majeure -- meaning it cannot meet contractual supply obligations -- on its pipeline south of Marsh Island.

The company said it expected the force majeure to continue for at least another day while it checks the pipeline for damage.

The search continues for a missing crew member, the Coast Guard's Harless said.

"We have no plans to end the search soon," he said.