Australia is investigating two objects seen on satellite images that could potentially be linked to the missing Malaysia Airlines plane, officials say.
Planes and ships from Australia, New Zealand and the US were heading to the area 2,500km (1,550 miles) south-west of Perth to search for the objects.
The largest appeared to be 24m in size, maritime authorities said, but warned they could be unrelated to the plane.
Australia has been searching in the southern Indian Ocean for the aircraft.
Malaysia Airlines flight MH370 was flying from Kuala Lumpur to Beijing on March 8 when it lost contact with air traffic controllers. A total of 239 people were on board.
Twenty-six nations have been involved in a major search for the missing plane, which Malaysia says was intentionally diverted.
Investigators have been scrutinising the backgrounds of both the crew and the passengers, but have so far identified no evidence of terror or other potentially relevant links.
A number of sightings of possible debris have been investigated in the course of the search but so far none have proved to be linked.