Recovering debris from the Malaysian Airlines plane is vital to finding out what caused it to go missing and to prevent a repeat, as well as providing some closure for the families of passengers on board. In the absence of evidence, speculation over possible causes ranges widely, including terrorist attack, pilot error and plane malfunction.
The plane vanished off radar screens early Saturday morning en route to Beijing from Kuala Lumpur at 35,000 feet (11,000 meters), roughly in between the east coast of Malaysia and that of southern Vietnam. The airline says the pilots didn't send out any distress signals, suggesting a sudden and possibly catastrophic incident.
In a statement, Malaysia Airlines said the western coast of the country, near the Straits of Malacca, was "now the focus'' of the hunt. That is on the other side of peninsular Malaysia from where flight 370 was reported missing, meaning if the plane went down there it would have had to fly over the country.
Malaysia's air force chief said Sunday there were indications on military radar that the jet may have done a U-turn.
Civil aviation chief Azharuddin Abdul Rahman said the Malaysia Airline statement didn't imply authorities believed the plane was now more likely to be off the western coast. "The search is on both sides,'' he said.
China, where two-thirds of the passengers were from, has urged Malaysian authorities to "speed up the efforts'' while also contributing ships and helicopters to the search.
A shopping mall in Beijing suspended advertising on its large outdoor LED screen to display a search timer _ an image of an airplane along with a digital clock marking the time since contact with the flight was lost.
Speculation that it might have been a terrorist attack has been heightened by the fact that two passengers are known to have boarded the flight using passports stolen in Thailand. Authorities questioned travel agents Monday at a beach resort in Thailand who police say were involved in handling reservations and issuing tickets used by two men. The identities of the pair, who had both booked onward flights to Europe, aren't yet known.
More than 40 planes and ships from over 10 nations are involved in the search, methodically combing sections of the ocean. Assuming it crashed into the ocean or disintegrated in midair, there will likely still be debris floating on the ocean, but it may be widely spaced out and the bulk of it may have already sunk.
The United States has sent two navy ships, at least one of which is equipped with helicopters, and a Navy P-3C Orion plane that onboard sensors allow the crew to clearly detect small debris in the water. It said in a statement that the Malaysian government had done "tremendous job'' organizing the land and sea effort.
The hunt began on Saturday morning at the point the plane was last known to be. But with no debris found, the search has been systematically expanded to include areas where the plane could have in theory ended up given the amount of fuel it had on board. That is an area many thousands of square kilometers (miles) wide.
Vietnamese planes and ships are a major component of the international search and rescue effort.
Lt. Gen. Vo Van Tuan, deputy chief of staff of Vietnamese People's Army, said authorities on land had also been ordered to search for the plane, which could have crashed into mountains or uninhabited jungle. He said that military units near the border with Laos and Cambodia had been instructed to search their regions also.
"So far we have found no signs (of the plane) ... so we must widen our search on land,'' he said.