(Mariner Energy item updated with further information on the accident at the company's Vermillion platform.)

NEW YORK ( TheStreet) -- A fire broke out on an offshore platform owned by Mariner Energy ( ME) in the Gulf of Mexico, a region still reeling from the aftereffects of the massive BP ( BP) oil-spill disaster -- but whether the accident has caused a leak remains unclear.

Workers were sandblasting the platform when the fire occurred, and production had been halted, a Mariner Energy spokesman told CNBC Thursday morning.

All 13 of the platform's crew were accounted for, and no injuries were reported.

The spokesman also said there was neither evidence of a spill, nor any visible sheen on the surface of the water. Later in the day, Mariner issued a statement saying that after an "initial flyover, no hydrocarbon spill was reported."

But the U.S. Coast Guard told the AP Thursday that it had located a slick not far from the Mariner platform. The slick measured a mile long and about 100 feet wide, according the Coast Guard.

Other reports indicate that the fire is still burning as of Thursday afternoon.

According to New Orleans' WDSU, the accident occurred Thursday morning, and rescue vessels from both Houston and New Orleans have responded.

The platform, situated in shallow water 100 miles off the coast of Louisiana in the Gulf, was producing about 9.2 million cubic feet of natural gas per day and 1,400 barrels of oil and condensate, according to the company's press release. It and another Mariner-owned well on the same oil-and-gas block, called Vermillion 380, produced 1.1 billion cubic feet of gas in 2009.

Shares of Mariner, which is in the process of being acquired by Apache Energy, promptly sold off in frantic trading after the news broke, dropping nearly 11%.

By Thursday afternoon, as more details emerged that appeared to allay fears of a catastrophic accident, the stock retraced some of those losses. Mariner shares closed Thursday at $22.75, down 2.6%. Volume surpassed 44 million, nearly 10 times the daily average.

-- Written by Scott Eden in New York

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