To produce LNG, natural gas is cooled down to around minus 160 degrees Celsius, so facilities must be chilled before oil rig flanges gulf coast production can begin, typically by using fuel from other sites. Taking such a step indicates the plant, in northern Australia's Darwin, is getting closer to starting output.

The LNG tanker 'Pacific Breeze' is currently in the Java Sea and expected to reach Darwin on April 26, with a draft of 93 percent, suggesting it is almost full, according to Thomson Reuters Eikon ship tracking data. The ship has the capacity to carry up to 182,000 cubic metres of LNG, according to Inpex.

A spokesman for Inpex said the vessel had been chartered to transport LNG bought from another LNG project with the objective of cooling the onshore Ichthys LNG plant ahead of the project's start-up.

He added the vessel's LNG could also possibly be used as a first gulf coast oil rig export cargo should Ichthys experience further delays in production, but stressed this had not yet been decided.

The more than $37 billion Ichthys project has seen several delays and cost overruns of billions of dollars due to technical difficulties.

Inpex, Japan's top oil and gas producer, said in March it had postponed its latest planned start-up to April or May. The start was originally slated for 2016.

The newly-built Pacific Breeze is contracted to supply 1.75 million tonnes a year of LNG from Ichthys to Taiwan's CPC Corp.

CPC did not respond to queries for comment.

The vessel loaded a cargo in Singapore in late March after conducting sea trials.

Once the Central Processing Facility is commissioned at Ichthys, it will produce condensate - an ultra-light form of crude oil - before LNG, Inpex has said without giving a specific timeframe.

Taiwan's CPC, the biggest customer of Ichthys, is scheduled to take delivery of its first LNG cargo in the second half of this year, a source familiar with the matter said, declining to be identified.

Other customers of the project mainly include Japanese utilities.

Inpex holds 62.245 percent of Ichthys, France's Total 30 percent, with the rest spread amongst Taiwan's CPC Corp and Japanese utilities Tokyo Gas, Osaka Gas, Kansai Electric, JERA Corp and Toho Gas .