SYDNEY (Reuters) - A leaking Australian oil well is likely to pour oil into the Timor Sea for nearly two months before it can be stopped, the operator said on Sunday, as environmentalists expressed grave fears for rare wildlife.

Rig operator PTTEP Australasia said it planned to drill a relief well and pour mud to stop the leak, which began on Friday with a blow-out more than three kilometers (two miles) deep.

It would take 20 days to bring a new offshore drilling rig by barge from Singapore, plus four weeks to drill, the company said in a statement.

Asked if this meant the well would flow for nearly two months, a company spokesman told Reuters: “That is pretty much the estimation.”

Environmentalists have expressed concern about the giant slick, saying the entire area is ecologically significant and part of an “ocean super highway” for migrating animals between the Indian and Pacific Oceans.

Many breathe air and could surface in the oil, an official of WWF Australia said.

Earlier on Sunday the Australian Maritime Safety Authority used C-130 Hercules aircraft to spray dispersant chemicals on the slick, which was in excess of 8 nautical miles in length.

Spokeswoman Tracey Jiggins said the results were encouraging but the agency was prepared for a long operation.

PTTEP Australasia, a unit of Thailand’s PTT Exploration and Production PCL, said a team of international experts recommended drilling a relief well, to intersect the existing well and stop its flow.

Company spokesman Ian Williams gave no estimate of the amount of oil that would be released, but said the company believed it would be possible to prevent the slick spreading.

“There is a blow-out of some kind. It is very deep,” Williams told Reuters, putting the depth at around 3,500 meters.

An air exclusion zone had been set up and ships advised to stay more than 20 nautical miles away from the rig, considered too dangerous to board.

WWF Australia called for changes to ensure better preparations for such disasters, noting it took three days for the first dispersant to be sprayed.

“From a global scale this is one of the most important places on the planet for ocean wildlife,” Gilly Llewelyn, WWF Australia’s director of conservation, told Reuters.

Among the animals affected were three endangered species of turtles, plus sea snakes, she said. Even a pygmy blue whale has been monitored there.

“It seems to be one of these critical migration routes -- an oceanic super highway,” she said.

The spill occurred at the Montara development, a project due to come on stream later this year. The West Atlas drilling unit is owned by Norway’s SeaDrill Ltd, but operated by PTTEP Australasia.

The location has been given as about 250 km (155 miles) off the far north Kimberley coast of Western Australia state.

Australia’s official overseer for the petroleum industry, the National Offshore Petroleum Safety Authority, was investigating the incident.