Australian authorities were Sunday ordered to help extinguish a fire which broke out on a leaking oil rig that has been pumping thousands of barrels of oil into the Timor Sea for months.

Energy Minister Martin Ferguson directed the National Offshore Petroleum Safety Authority to "extend every possible assistance" to respond to the blaze on the West Atlas rig off Australia's northwest coast.

Australia's Maritime Safety Authority will also support efforts to quell the fire on the drilling rig which has been spewing up to 400 barrels of oil into the ocean each day since August 21, he said.

"Fire broke out on the West Atlas drilling rig and the Montara wellhead platform after the West Triton successfully intercepted the leaking well this morning," Ferguson said.

"Well kill operations were under way at the time, but have now been suspended.

"Current operations are focused on reducing the intensity of the fire."

The rig's Thai-based operator, PTTEP Australasia, said specialists had finally succeeded in the first stage of plugging the well at 9:30 am (0130 GMT) after weeks of failed attempts.

"They had not actually stopped or killed the leak... and then unfortunately the fire broke out," a company spokeswoman told AFP.

PTTEP said all 113 personnel working on the West Triton rig at the isolated site some 250 kilometres (155 miles) offshore had been reported safe and non-essential staff were being evacuated. No workers have been on the West Atlas since it began leaking.

The company gave no indication of the severity of the blaze but said a fire-fighting vessel, the Nor Captain, had sprayed water onto the fire but had now moved two nautical miles off the rig.

"Seawater is also being pumped down the relief well from the West Triton rig in an effort to 'wet' the gas and help bring the fire under control," PTTEP said in a statement.

The rig's operators have been struggling for weeks to stop the leak, which environmentalists fear poses long-term risks to the area's wildlife.

"The government remains deeply concerned about this incident," Ferguson said in a statement.

"From day one our top priorities have been the safety of people and the protection of the environment. Stopping the flow of oil and gas safely and as soon as possible remains our prime objective."

On Friday, a biologist commissioned to carry out an Australian government survey of the West Atlas drilling rig found that the massive spill posed an immediate risk to dozens of marine species.

"It is possible that species that are dying or dead and lying in oil-affected water may not stay afloat for long periods of time, making it unlikely that we would find large numbers of dead animals," James Watson wrote.

The operation to stem the leak has involved PTTEP towing the West Triton rig from Singapore to the site, a process which took five weeks, to drill down some 2.6 kilometres under the seabed to the source of the emissions.

Specialists then had to intersect a casing 25 centimetres in diameter using sophisticated electro-magnetic ranging tools, before they could begin plugging the leak with heavy mud.

PTTEP has said it will meet the full costs of the Australian Maritime Safety Authority's clean-up operation but conservation groups have been critical of the response to the oil spill.