Monitoring the clean-up of a huge oil spill in pristine Australian waters could take as long as seven years, an official said Wednesday as environmentalists urged a wide-ranging inquiry into the disaster.

As many as 28,000 barrels of oil have gushed into the Timor Sea off Western Australia's northern coast in the 10 weeks since the West Atlas oil rig began leaking, raising concerns of an environmental disaster.

Attempts to plug the hole were delayed by the need to bring equipment from Singapore, the difficulty of the operation some 2.6 kilometres (1.6 miles) below the seabed and a fierce inferno fuelled by the leak which erupted Sunday.

The rig's operator PTTEP Australasia said the clean-up would be carried out quickly after the oil and gas leak and the fire were shut down on Tuesday.

"I suspect a couple of months is what we are sort of anticipating," the company's Jose Martins said of the operation.

"The environmental plan really could take up to seven years."

Resources and Energy Minister Martin Ferguson, who has called for an inquiry into the incident, welcomed the news that the fire on the rig and the Montara wellhead platform had been extinguished.

"I think we are all relieved that what could have been a very dangerous situation hasn't seen any loss of life," the minister told state radio.

Environmentalists said stopping the flow was the first step in cleaning up the spill some 250 kilometres offshore, but called for any inquiry into the leak and fire to have wide-ranging powers.

"This is a major spill," WWF Australia's Ghislaine Llewellyn told AFP. "This is up in the top three in Australian history."

Llewellyn said the spill of oil and condensate combined with the dispersant used to control the slick had created a toxic cocktail which would have a long-term impact on the area's pristine tropical marine life.

Authorities said they were investigating whether oil from the rig could have washed up on Australia's northern coast.

The Australian embassy in Jakarta has dismissed reports that oil from the leak had come close to Indonesian coastal waters as "highly unlikely".