The disappearance of a Malaysian jetliner is an "unprecedented aviation mystery", a senior official said today, with a massive air and sea search now in its third day failing to find any confirmed trace of the plane or the 239 people aboard.
The head of Malaysia's Civil Aviation Authority, Azharuddin Abdul Rahman, said a hijacking attempt could not be ruled out as investigators explore all theories for the loss of Malaysia Airlines flight MH370 en route to Beijing.
"Unfortunately we have not found anything that appears to be objects from the aircraft, let alone the aircraft," he told a news conference.
As dozens of ships and aircraft from seven countries scour the seas around Malaysia and south of Vietnam, questions mounted over possible security lapses and whether a bomb or hijacking attempt could have brought down the Boeing 777-200ER airliner.
Hopes for a breakthrough rose briefly when Vietnam scrambled helicopters to investigate a floating yellow object it was thought could have been a life raft. But the country's Civil Aviation Authority said on its website that the object turned out to be a "moss-covered cap of a cable reel".
Interpol confirmed at least two passengers used stolen passports and said it was checking whether others aboard had used false identity documents.
Flight MH370 disappeared from radar screens in the early hours of Saturday, about an hour into its flight from Kuala Lumpur, after climbing to a cruising altitude of 35,000 ft (10,670m).
Underlining the lack of hard information about the plane's fate, a US Navy P-3 aircraft capable of covering 1,500 sq miles every hour was sweeping the northern part of the Strait of Malacca, on the other side of the Malaysian peninsula from where the last contact with MH370 was made.
"Our aircraft are able to clearly detect small debris in the water, but so far it has all been trash or wood," said US 7th Fleet spokesman Commander William Marks in an emailed statement.
No distress signal was sent from the lost plane, which experts said suggested a sudden catastrophic failure or explosion, but Malaysia's air force chief said radar tracking showed it may have turned back from its scheduled route before it disappeared.
A senior source involved in preliminary investigations in Malaysia said the failure to quickly find any debris indicated the plane may have broken up mid-flight, which could disperse wreckage over a very wide area.
"The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at 35,000 feet," said the source.
Asked about the possibility of an explosion, such as a bomb, the source said there was no evidence yet of foul play and that the aircraft could have broken up due to mechanical causes.
The United States extensively reviewed imagery taken by American spy satellites for evidence of a mid-air explosion, but saw none, a US government source said.
Boeing declined to comment and referred to its brief earlier statement that said it was monitoring the situation. The Boeing 777 has one of the best safety records of any commercial aircraft in service.
About two-thirds of the 227 passengers and 12 crew now presumed to have died aboard the plane were Chinese. The airline said other nationalities included 38 Malaysians, seven Indonesians, six Australians, five Indians, four French and three Americans.