The oil spill forced an evacuation to Darwin of all 69 workers from the West Atlas rig, PTTEP Australasia said.
The oil and gas spill off Western Australia's Kimberley Coast is much larger and closer to the coast than previously reported, the Australian Greens say.
The clean-up of the August 21 spill is being managed by the Australian Maritime Safety Authority (AMSA).
After visiting the PTTEP Australasia West Atlas oil rig spill, Greens senator Rachel Siewert said it was much bigger and closer to the coast than first reported.
Click for more photos
The West Atlas Oil Spill
The massive fire that engulfed the West Atlas rig last week after workers tried to plug an oil leak. Photo: supplied
"There is a film of oil around the rig, and from horizon to horizon. From east to west it stretches 180km at a minimum," she said.
An AMSA spokesman said the authority would not comment on the size of the spill on Friday night but would release further information soon.
A drilling rig, moored on Batam Island in Indonesia, left for the West Atlas oil rig at 4.45pm (AEST) on Thursday, PTTEP said in a statement on Friday.
"Favourable conditions mean the West Triton is now expected to reach the West Atlas and commence drilling activities inside of the previously advised timeframe (16 days)," the company said.
Two tugs will tow the rig to within two kilometres of the Montara well head platform, where it will drill a relief well to stop the leak.
A Boeing 747 is expected to leave on Saturday to fly in high capacity pump and spray equipment from Singapore.
Woodside has contacted the federal government to offer the use of a drill rig and emergency response team.
Senator Siewert said PTTEP should be compelled to take up Woodside's offer of a closer rig, which would stop the spill much sooner.
PTTEP directed AAP to AMSA when contacted for comment on the size of the spill.
AAP
