RAAF aircraft searching for Malaysia jet

A second RAAF aircraft is leaving Darwin to join the search for the missing Malaysia Airlines jet.

Six Australians and two New Zealanders, one who lives in Perth, are feared dead after the Boeing 777-200 disappeared over the South China Sea early on Saturday morning, one hour into what should have been a six-hour flight from Kuala Lumpur to Beijing.

Authorities are examining links to terrorism, with two of the flight's 239 passengers found to be using stolen passports.

Australia sent a RAAF AP-3C Orion on Sunday night and a second is leaving Darwin at 8.30am (AEDT) on Monday.

Air Marshal Mark Binskin said the maritime patrol and long-range surveillance aircraft are equipped with sensors and electro-optics detectors that are ideal for the operation.

There are 18 Australian crew members on board each RAAF jet.

Foreign Minister Julie Bishop has been in touch with her Malaysian counterpart to offer Australia's support.

She said reports of stolen passports were concerning.

"There may be no connection at all but it is a worrying development," Ms Bishop told ABC radio on Monday.

"Our officials are in urgent and ongoing contact with authorities in Malaysia."

Malaysia has set up a rescue co-ordination centre and dozens of ships and aircraft are looking for the wreckage, she said.

Vietnam, the Philippines, US, Singapore and China have also sent resources to join the search.

Families of missing Australians on board are receiving consular assistance, Ms Bishop said.