No threat to Cocos fuel supply: Defence

Defence has played down the threat of border air patrols being disrupted by rising ocean waters swamping a fuel depot on Cocos Islands.

There are concerns coastal erosion could result in the depot's six fuel tanks, which have the capacity to hold 10 million litres of aviation fuel and diesel, becoming submerged as early as mid-year.

A combination of erosion and a king tide resulted in sea water lapping at the depot in December.

A P-3C Orion maritime patrol aircraft is permanently based on the remote Indian Ocean islands for surveillance of asylum seeker boats.

If the depot cannot operate, Defence may be forced to use an alternative refuelling base in northwest Western Australia or even in Indonesia.

Limited fuel storage capacity on Christmas Island rules it out as a base for patrol aircraft.

Asked about the ramifications of the erosion on Operation Sovereign Borders, a Defence spokeswoman told AAP it believed "there is no immediate threat to fuel supply".

It would continue to liaise with the regional development department and fuel supplier Shell to ensure the operational needs of the Australian Defence Force were met.

Defence chiefs met with Shell representatives in December to discuss the problem.

The Shire of Cocos has recruited five unemployed Cocos-Malay residents to fill hundreds of giant sandbags, which weigh 1.7 tonnes when full, to build a sea wall to protect the fuel depot.

Work is expected to be completed by the end of March, subject to weather and maritime conditions.