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.
(Read more: Why a high-tech jet is so hard to find)
"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.