BG Group said this milestone marked the successful completion of laying down the longest large-diameter buried pipeline in Australia over the past two years.

"To have first gas on Curtis Island in a little over three years from project sanction is an immense achievement,” BG CEO Chris Finlayson said.

“It is a testament to the expertise and dedication of everyone working on this vast and complex mega-project.”

The project’s further progress will be followed by the global LNG scene with plant commissioning to take place during the March quarter.

"Delivering this key milestone demonstrates the advanced stage of development at the world’s first coal seam gas to LNG project,” Finlayson said.

“We are now entering the final construction and commissioning phases and we remain firmly on track to deliver first commercial LNG in the second half of 2014, as scheduled and within the $20.4 billion budget.

"We have overcome many challenges along the way, and we still have more hard work in front of us, but last February I set the tough target to have first gas on Curtis Island by the end of this year, and I am delighted that we have met it."

The two-train project is targeting 8.5 million tonnes per annum of capacity next year with significant partner China National Offshore Oil Corporation also being the key offtake party.

Technical feasibility of CSG-to-LNG operations for this project also builds expectations for the Gladstone LNG and Australia Pacific LNG projects on the island.

The Arrow LNG project has become less certain over recent months and there is speculation it could integrate with one of the other Curtis Island-based projects.