Sydney  - Firefighters battled to put out a fire at an oil-and-gas rig in the Timor Sea north of Australia Tuesday by pumping thick mud into the well to plug the leak.

The fire broke out Sunday with flames and smoke rising hundreds of metres into the air as oil workers tried to stop a leak from the rig which occurred 10 weeks ago.

The leak released 400 barrels of oil a day into the ocean leaving a massive oil slick spreading across the previously pristine waters of the Timor Sea, threatening marine life.

The Thailand-owned operators of the West Atlas rig, PTTEP Australasia, is mixing 4,000 barrels of heavy mud to pour down a relief well dug nearby.

PTTEP spokesman Jose Martins told reporters in Perth it was not known how the fire broke out, but the mud should cut off the supply of oil and gas and strangle the fire.

The Australian government has ordered a full inquiry into the disaster which is to get underway once the fire is out the leak plugged.

However, World Wildlife Fund spokesman Paul Gamblin was concerned the inquiry may not make public all the reasons behind the disaster, in an effort to protect the lucrative oil and gas industry. (dpa)