The prime minister says the public shouldn’t jump to conclusions over the Malaysia Airlines plane disappearance and speculated links to terrorism.

Australians shouldn’t fear flying despite speculated terrorism links to the ill-fated Malaysia Airlines flight, Prime Minister Tony Abbott says.

Travel warnings haven’t been upgraded and Mr Abbott has been careful not to encourage a climate of fear.

The two day multi-national search, including two Australian planes, has found large oil slicks but provided few clues to what led to one of the most baffling aviation disasters in recent memory.

Six Australians and two New Zealanders are among 239 people feared dead aboard the Kuala Lumpur to Beijing flight.

A terrorism investigation is underway amid revelations two passengers travelled on false passports but Mr Abbott called for calm.

“Very occasionally we have disasters that have a more sinister cause but I am just not going to feed any speculation about this,” he said.

“Australians are not a timid people, never have been, never will be, and the last thing I would want to do is to discourage travel.

“Tourism is important, trade is even more important and I would encourage Australians who have business in our region, whether its for pleasure or for work, I would encourage people to just go about their ordinary business at this time.”

Relatives of the Australian and New Zealand passengers are clinging to hope, while also acknowledging their worst fears are likely to eventuate.

Brisbane couples Cathy and Bob Lawnton and Rodney and Mary Burrows are feared lost after the long-time friends set off on a the trip of a lifetime.

In a statement, the Lawnton family said they were preparing for the worst.

“All the family members are trying to remain positive for any hope of survivors (but) we are bracing ourselves for the worst possible outcome.”

Ms Burrows served as a civilian employee at Queensland police for 16 years and colleagues held a prayer vigil on Monday.

“We are hoping against all hope that they might be found alive,” Police Commissioner Ian Stewart said.

“But as the time goes on, obviously the potential tragedy of what has occurred is not lost on the organisation.”

The Sydney couple aboard the flight, Yuan Li and Naijun Gu, were believed to be on their way to spend time with their baby and toddler, who were being looked after by grandparents in China.

The couple sold their Sylvania home in November and last week their petrol station business was placed into liquidation.

New Zealander Paul Weeks, a 39-year-old mechanical engineer based in Perth, was travelling to Mongolia for his first shift of a fly-in-fly-out job.

His distraught wife Danica is desperate for information from Malaysian authorities but has to care for their two young sons and can’t travel.

“They’re just not telling us anything,” she said.