NEW ORLEANS, Louisiana (AFP) Ã¢â‚¬â€œ A blazing oil rig sank Thursday into the Gulf of Mexico sparking fears of an environmental disaster almost two days after a massive blast that left 11 workers missing.

Oil fires had been raging on the Deepwater Horizon rig for more than 36 hours since a spectacular explosion late Tuesday that sent huge balls of flame leaping into the night sky.

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The US Coast Guard was frantically searching for those still missing after the other 115 workers on board the platform were brought safely back to the United States mainland and reunited with their families.

Thursday’s sensational development brought fears of massive pollution from the stricken rig as it sank beneath the surface some 50 miles (80 kilometers) off the Louisiana coast, still apparently pumping oil.

Before the explosion there were 700,000 gallons of diesel fuel on board the semi-submersible platform and it had been drilling 8,000 barrels, or 336,000 gallons, of oil a day.

“Worst case scenario, there is a potential environmental threat,” Coast Guard spokeswoman Katherine McNamara told AFP.

Firefighting vessels had spewed out thick streams of water at the rig in a vain bid to control the blaze and keep the sharply tilting platform afloat as large columns of black smoke shot up into the sky.

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Any pollution would be far smaller than the 1989 Exxon Valdez oil tanker spill, considered one of the worst man-made environmental disasters.

The Exxon Valdez poured nearly 11 million gallons of crude into Alaska’s Prince William Sound, devastating some 750 miles (1,300 kilometers) of its once pristine shores.

Rescue crews for the current disaster toiled throughout the night, scouring some 1,940 square miles (5,025 square kilometers) of sea. A helicopter and a plane resumed the aerial search at first light.

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Seventeen workers were airlifted to hospital on Wednesday after suffering broken bones, burns and smoke inhalation in the explosion on the semi-submersible, mobile rig. Four remained in critical condition.

But there was no sign of the missing workers and it remained unclear whether they made it safely into one of the rig’s lifeboats.

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“We’re going to continue to search as long as there is a reasonable probability of finding them alive,” coast guard spokeswoman Ashley Butler told AFP, adding that weather conditions were favorable for the search.

After the blast, workers jumped up to 100 feet (30 meters) into the water and scurried for safety, most of them making it to lifeboats to be picked up by rescuers and taken to Port Fourchon on the Louisiana mainland.

The 396-by-256-foot (121-by-78-meter) platform, owned by Transocean, Ltd. and under contract to BP, was still ablaze but officials said environmental damage appeared to be minimal because the fire was burning much of the spilt fuel.

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Transocean, based in Houston, Texas, is the world’s largest offshore drilling contractor, with a fleet of 140 mobile offshore drilling units, in addition to three ultra-deepwater units under construction.

Transocean vice president Adrian Rose said the rig likely suffered a blowout while drilling through rock at oil giant BP’s Macondo prospect, although investigations into the exact cause of the accident are ongoing.

A total of 126 people were onboard the platform at the time of the explosion, 79 of them Transocean staff, six BP personnel and 41 contractors.