About 30 ships and 21 aircraft from Indonesia, Australia, Malaysia, Singapore and South Korea would search up to 10,000 square nautical miles on Tuesday, officials said.

Indonesia's air force spokesman, Hadi Tjahjanto, said authorities would investigate an oil spill seen on Monday, although a separate possible slick turned out to be a reef.

Searchers had investigated several areas where possible debris had been sighted in the water but had found nothing connected to the missing plane, Tjahjanto told Reuters.

Authorities would also investigate reports from fishermen of an explosion on Sunday morning off an island in the area, Tjahjanto added, although dynamite fishing is common in Indonesian waters.

The US military said the USS Sampson, a guided missile destroyer, would be on the scene later on Tuesday.

"We stand ready to assist in any way possible," Pentagon spokesman Mark Wright said.

COULD PLANE HAVE STALLED?

Flight QZ8501 had sought permission from Indonesian air traffic control to ascend to avoid clouds just before it went missing.

Online discussion among pilots has centred on unconfirmed secondary radar data from Malaysia that suggested the aircraft was climbing at a speed of 353 knots, about 100 knots too slow, and that it might have stalled.

The plane, whose engines were made by CFM International, co-owned by General Electric and Safran of France, lacked real-time engine diagnostics or monitoring, a GE spokesman said. Such systems are mainly used on long-haul flights and can provide clues to airlines and investigators when things go wrong.

Officials said the sea in the general search area was only 50 to 100 (150 to 300 feet) metres deep, which should help in finding the plane.

"The Java Sea area where they are now searching isn't even an ocean, it's more of an inland sea," Erik van Sebille, a physical oceanographer at the University of New South Wales in Sydney told Reuters.

"It's so shallow that they may just be able to spot the plane," said van Sebille, noting that sunlight travels through water up to about 100 metres.

Oceanographer Pattiaratchi said debris would normally be expected to float for about 18 days before sinking.