aircraft and 40 ships have been deployed to the area by Malaysia, Thailand, Australia, Singapore, Indonesia, China and the United States, in addition to Vietnam's fleet.
Vietnamese air force jets spotted two large oil slicks Saturday, but it was unclear whether they were linked to the missing plane.
Two-thirds of the jet's passengers were Chinese. The rest were from elsewhere in Asia, North America and Europe.
After more than 30 hours without contact with the aircraft, Malaysia Airlines told family members they should ``prepare themselves for the worst,'' Hugh Dunleavy, the commercial director for the airline, told reporters.
Finding traces of an aircraft that disappears over sea can take days or longer, even with a sustained search effort. Depending on the circumstances of the crash, wreckage can be scattered over many square kilometers (miles). If the plane enters the water before breaking up, there can be relatively little debris.
A team of American experts was en route to Asia to be ready to assist in the investigation into the crash. The team includes accident investigators from the National Transportation Safety Board, as well as technical experts from the Federal Aviation Administration and Boeing, the safety board said in a statement.
Malaysia Airlines has a good safety record, as does the 777, which had not had a fatal crash in its 19-year history until an Asiana Airlines plane crashed last July in San Francisco, killing three passengers, all Chinese teenagers.