The MH370 Malaysia Airlines flight from Kuala Lumpur to Beijing, with more than 150 Chinese and five Indians aboard, went missing over South China Sea on Saturday.
A multinational rescue effort has yet to stumble upon any wreckage and other than an oil slick, there is no indication plane had crashed.
France's air accident board, which led a three-year investigation into the 2009 loss of an Air France jet in the Atlantic, has offered to help Malaysia and Vietnam with the recovery of a missing Malaysia Airlines plane.
"We have communicated to Malaysian and Vietnamese authorities that we are ready to assist with the underwater search operations or recovery of wreckage," a spokeswoman for the Paris-based BEA accident investigation branch said on Sunday.
The US National Transportation Safety Board has also offered to help with the recovery of the Boeing 777.
Reuters reported that officials investigating the disappearance of the Malaysia Airlines jetliner suspect it may have disintegrated in mid-flight, as Vietnam reported a possible sighting of wreckage from the plane.
Read: Passport thefts deepen mystery of Malaysia jet, Vietnam search team spots suspected debris
Read: 'Oil slicks offer sign that Malaysian jet crashed'
Arni Marlina, 36, a family member of a passenger onboard the missing Malaysia Airlines flight MH370, cries at a hotel in Putrajaya. (Reuters photo)
"The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at around 35,000 feet," said the source, who is involved in the investigations in Malaysia.
If the plane had plunged intact from such a height, breaking up only on impact with the water, search teams would have expected to find a fairly concentrated pattern of debris, said the source, speaking on condition of anonymity because he was not authorised to speak publicly on the investigation.
The source was speaking to Reuters shortly before Vietnamese authorities said a military plane had spotted at sea an object suspected to be part of the missing airliner.
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 issues.
"We received information from a Vietnamese plane saying that they found two broken objects, which seem like those of an aircraft, located about 80 km to the south-west of Tho Chu Island," a senior official from the National Committee for Search and Rescue, who did not wish to be named, told AFP.
"As it is night, they cannot fish them out for proper identification. They have located the position of the areas and flown back to the land," he added.
Planes and boats would be sent back to the area Monday to investigate further, he said.
Read: Relatives of Indian passengers hover between despair and fragile hope
Malaysian authorities have said they are focused on finding the plane and have declined to comment when asked about the investigations.
A Chinese relative of passengers aboard a missing Malaysia Airlines plane cries while leaving a hotel room for relatives or friends of passengers aboard the missing airplane, in Beijing. (AP photo)
Read: Malaysian airline may have turned back, says Air force chief
Read: US to assist in Malaysia air crash investigation
Reports said Malaysian authorities were investigating the identities of two more passengers aboard the flight, who used stolen passports, meaning that at least four people on the plane got through security with stolen IDs.
One of them was travelling on the passport stolen in Thailand in August last year from 37-year-old Italian national Luigi Maraldi. Authorities confirmed Maraldi was alive and currently in Thailand.
The second stolen passport belongs to Christian Kozen, a 30-year-old Austrian. It had been stolen two years ago when Kozen was traveling in Thailand.
BBC reported the two people travelling on stolen passports had bought their tickets at the same time and were booked on flights from Beijing to Europe.
In a sharply worded criticism of shortcomings of national passport controls, Interpol said no country checked its database that held information about the two stolen passports, AP reported.
According to Interpol, information about the thefts was entered into its database after they were stolen in Thailand.
Read: Malaysian jet's disappearance among rarest of aviation disasters
Read: A look at world's deadliest air disasters
The Lyon, France-based international police body said in a statement it was investigating all other passports used to board flight MH 370 and was working to determine the "true identities" of the passengers who used the stolen passports.
Malaysian authorities, however, were cautious about the terror angle. At a packed press conference on Sunday afternoon, Malaysia Airline spokesperson Ong Ming Choy said no information has been confirmed so far to suggest terrorism was behind the loss of contact with the flight.
Reuters, however, quoted an official with "direct knowledge of the investigation" as saying that "early indications show some sort of a security lapse, but I cannot say any further right now".
But for all the speculation about terror links, the most important part of the puzzle – the aircraft itself – remained bafflingly missing.
Director general of the Malaysian Maritime Enforcement Agency admiral Mohd Amdan Kurish, left, checks a radar during a searching for the missing Malaysia Airlines plane in Kelantan, Malaysia. (AP photo)
Philippine military said the initial search for the missing Malaysian aircraft was unsuccessful till Sunday afternoon; the Singaporean defence ministry told China's official news agency, Xinhua, they had not received any report about the discovery.
The Vietnamese military told their state media that it had dispatched a helicopter to an area where "suspicious floating objects" were spotted for further investigation,
It has been a long and till now futile search for the air force and navies from several east and south-east Asian countries including China looking for signs of the aircraft.
Latest reports said the search efforts were being focused on the coast off southern Vietnam.
Though weather in South China Sea is expected to remain normal, it is possible that strong sea currents could sweep away debris — if the flight has indeed crashed into the sea — further away from the original site of impact.
For the family members of the passengers, the wait for credible and definitive information has not only been long but also an agonising one.
Many relatives have been put at an east Beijing hotel by the airlines. Many more poured into the hotel for more information on Sunday.
Meanwhile, two Chinese warships with 52 marines and a medical team have been dispatched to the possible site of incident, state media reported.
"The amphibious landing ship "Jinggangshan", loaded with life-saving equipments, underwater detection facilities and supplies of oil, water and food, set out from Zhanjiang port of south China's Guangdong Province at about 3am on Sunday for search and rescue mission," official news agency, Xinhua reported.
The vessel carries a 14-strong medical contingent and an underwater rescue team consisted of 10 divers.
Another Chinese navy frigate "Mianyang," was dispatched on Saturday night. Two helicopters as well as 52 marines, carrying assault boats and rubber dinghies, are on board.
Contact information for Malaysia Airlines:
Malaysia: +603 7884 1234
Beijing: +8610 6437 6249
Malaysia: +603 8777 5777
Five Indians on board missing Malaysia Airlines plane
Identity theft: Stolen European passports on missing Malaysian airline
China bound missing Malaysian flight presumed crashed
(With inputs from Reuters)