The search for missing Malaysia Airlines Flight MH370 entered day five on Wednesday, with focus centering on reports that the jet may have deviated from its original course.
No trace of the aircraft or the 239 passengers and crew has been uncovered so far, with conflicting reports about the whereabouts of the jet adding to the mystery.
NBC News reported Wednesday that US intelligence satellites detected no signs of an explosion around the time the plane went missing, which one official called "vexing." CNN quoted a Chinese government agency as saying its own satellites had observed a "suspected crash area" with three suspicious floating objects.
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The area of search for the missing aircraft has been expanded to 27,000 nautical square miles covering the South China Sea and Strait of Malacca, with a total of 12 countries participating in the operation, Malaysian authorities said late Wednesday.
There are a total of 42 ships and 39 aircraft currently involved in the multi-national search.
Malaysia's military are looking at the "possibility" that the airplane, which went missing on Saturday en route to Beijing from Malaysia's capital city Kuala Lumpur, turned back after flying over Kota Bharu on the Malaysian northeast coast, an official from the country's Transport Ministry told NBC News late Tuesday.
He added this was the reason why the search and rescue operation has been extended to cover the Malacca Strait. A Malaysian newspaper reported on Wednesday that local fishermen had found an orange-and-black life raft floating in the area, and reported it to authorities. The raft was emblazoned with the word "boarding".
Reuters cited a senior military officer late Tuesday as saying the jetliner turned and flew hundreds of kilometers to the west after it last made contact with air traffic control off the country's east coast. According to the source, the plane changed course after Kota Baharu, took a lower altitude and made it into the Malacca Strait.
(Read more: Timeline of Flight MH370)
However, the Malaysian Transport Ministry official told NBC by email that nobody from the country's military forces have said the plane took a low altitude or reached the Malacca Strait.
"The Malaysian authorities need to answer some questions as to why they have shifted the search, what it is about the radar traces that lead them to believe that the search areas should be to the west rather than the east," Andrew Herdman, director general at the Association of Asia Pacific Airlines in Los Angeles told CNBC.
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"Obviously, the larger the search area, the tougher it is to look for a needle in the haystack. When they double the radius, that quadrupled the area they were looking at, now it's even bigger, so I think we need more clarity as to what evidence is there from the radar traces, what is the trajectory of the aircraft after it stopped sending out signals," he added.
Malaysia Airlines Flight MH370 vanished from radar screens less than an hour after taking off from the Malaysian capital on Saturday. It was flying in good weather conditions and disappeared without a distress call – unusual for a modern jetliner.
Vietnam said early on Wednesday that it was scaling back its search in Vietnamese waters for the missing plane, Reuters reported.
Also on Wednesday, Bloomberg said Vietnam was dispatching ships to a fishing village 50 miles south of Ho Chi Minh City following reports of a plane on fire. Following investigation by the Vietnamese authorities, this had proved another dead-end.
Chinese government officials meanwhile discussed arrangement in Kuala Lumpur for Chinese families of passengers on Flight MH370.
"As of now, we have 115 family members in Kuala Lumpur and they are taken care of by 72 different caregivers," Malaysia Airlines said in a statement on Wednesday.
Relatives of the missing passengers are growing increasingly frustrated at the airline and the lack of clarity around how the situation unfolded.
During a meeting between the Malaysian government and Chinese relatives on Wednesday morning, it was revealed that "alright, good night" were the last heard words from the airline before it disappeared, Malaysian media reported.
The next media briefing is scheduled for 5 p.m. Kuala Lumpur time.
Terrorism not ruled out
Malaysia Airlines has said the pilots of MH370 did not send any distress signals, suggesting a sudden and possibly catastrophic incident. Speculation about what happened to the plan has ranged widely from pilot error to a plane malfunction, hijacking and terrorism.
John Brennan, the director of the Central Intelligence Agency, said on Tuesday that intelligence officials could not rule out terrorism as a factor in the disappearance of the Malaysia Airlines plane.
The secretary-general of international police agency Interpol said he believed it was unlikely that the missing flight was linked to terrorism.
He said the two passengers with stolen passports traveling on Flight MH370 were Iranians who had swapped their passports in Kuala Lumpur and used stolen Italian and Austrian passports to board the missing plane.
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Malaysia's police chief said earlier on Tuesday that the investigation into the missing Malaysian Airlines flight was focused on four main areas: terrorism, sabotage, personal and psychological problems.
Separately, Reuters reported that Malaysia Airlines was taking seriously a report by a South African woman who said the co-pilot of the missing aircraft had invited her and a female travelling companion to sit in the cockpit during a flight two years ago, in an apparent breach of security.
— By CNBC.com. Follow us on Twitter @CNBCWorld. NBC News, Reuters contributed to this report