CANBERRA - Australian federal government on Thursday expressed concerns about two Australians believed to have been held by Libyan authorities.

According to Department of Foreign Affairs and Trade (DFAT) Secretary Dennis Richardson, one of the Australians is a dual national who was arrested about a month ago, before the present political crisis erupted.

"Up until now we have been unable to make contact with that person," Richardson told a Senate estimates hearing in Canberra.

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Richardson said the second person of concern is an Australia who the DFAT believes was taken from a hotel in Tripoli by the Libyan authorities during the crisis.

Richardson said sketchy advice suggested the man's phone records showed he had been sending text messages about anti-regime protests.

"He along with a British national," he said. "Neither his company nor ourselves have been able to make contact with him ... or ascertain his whereabouts."

The government has been unable to make contact with a total of 10 Australians believed to be in Libya.

More than 50 Australians have already fled the country following the deadly clashes between protesters and leader Muammar Gaddafi's security forces.

Fifteen Australians are due to depart from Libya on a ferry bound for Malta on Thursday.

Another 36 or 37 have told DFAT they wish to leave the country, but Richardson said the government will not be chartering its own evacuation transport.

Instead, the Australians would be arranged to the evacuations conducted by the United States, Britain, Canada and Turkey.

"We believe the quickest and most effective means is through our partners," Richardson said.