SYDNEY: An oil rig burned uncontrollably off Australia Monday as officials warned the massive blaze could not be contained until they plug a leak which has gushed tonnes of crude over the past 10 weeks.

As the government ordered an inquiry into the emergency, environmentalists warned that delays in shutting down the fire and leak would further harm the pristine waters off the northwest coast, which are home to whales and dolphins.

The West Atlas rig caught fire Sunday during the latest attempt to stop the leak, which has dumped thousands of barrels of oil into the Timor Sea since it began leaching into the water on August 21.

The rig's operator, PTTEP Australasia, said stopping the leak was the only way to extinguish the blaze engulfing the deck and well head platform some 250 kilometres (155 miles) off the coast. It will launch another attempt Tuesday.

"The best and safest way to stop the fire is to 'kill the well' by pumping heavy mud into the leaking well," PTTEP director Jose Martins said.

"The mixture of heavy mud is designed to backflow along the leaking well, stopping the flow of gas and oil at the surface of the H1 well, cutting off the fuel source for the fire at the well head platform.

"This should kill the well and should stop the fire."

Resources and Energy Minister Martin Ferguson said the accident, the first on such a scale in 25 years of offshore drilling, had "clearly had an impact on the standing of the oil and gas industry in Australia".

"And I simply say that once the well is filled, the platform is made safe, I will conduct a full and independent enquiry to actually assess the cause of the incident and the manner in which it has been handled over the last 10 weeks."

A cameraman who flew over the site said the inferno was the biggest fire he had ever seen.

"It was so big we went round it two or three times, and in the end I just put the camera down and I just looked out the window and was awestuck by this thing," Stephen Cavenagh told Sky News.

Environmental groups have criticised the government's handling of the spill, saying it is threatening bird and marine life off Western Australia's resource-rich north coast.

"We are ranking it as a major environmental disaster," John Carey, a spokesman for the global Pew Environment Group, told AFP, adding that oil was a slow and silent killer for many marine species.

The area was a "marine superhighway for species moving in and out of the region so it's an area of global importance," he said.

"In terms of the greater northwest region, you are looking at up to almost one quarter of dolphins and whales in the world in this area."

Environmentalists such as WWF Australia's Ghislaine Llewellyn, who spent three days surveying the site, said the size and duration of the oil slick posed a high risk to marine and bird life in the area.

Llewellyn said in many cases there would be no dead animals lying on the water surface or washing up on to beaches because they would sink to the bottom if mired in the slick.

"Operating in a remote situation doesn't exempt the need for appropriate standbys, safeguards, backups all being to hand," she told AFP.

The Australian Marine Conservation Society said it hoped the government's inquiry would force the industry to improve its management of such accidents.

"We don't know why this disaster happened and we need to understand that to prevent this happening again in the future," the society's director, Darren Kindleyside, told state radio.