A terror threat was made against the Beijing Capital International Airport days prior to the abrupt disappearance of the Beijing-bound Malaysia Airlines flight MH370.

China Airlines has revealed they had alerted the authorities at the Civil Aviation Administration of China regarding the terror threat which was made on 4 March by an unknown man.

The airline operator's chief representative in Beijing, Peng Rong-min, said the unidentified man made the phone call threatening that a terrorist strike would take place at the Beijing airport.

The spokesperson added that they had informed the authorities concerned immediately after the call, the China Post reports.

The anonymous caller started off the conversation in French but later spoke in Mandarin as the China Airlines's staff do not understand French. He said he represented the East Turkestan Liberation Organisation; the authenticity of the phone call or the person's identity could not be verified.

As the mystery surrounding the sudden disappearance of the Boeing 777 continues to deepen, strong speculation that a terror strike had downed the aircraft is doing the rounds citing the travel by two passengers with stolen passports and fake identities.

However, investigators involved in the matter have so far said there is no direct evidence to corroborate the role of terrorism in the incident.

China has already appointed two separate teams to probe the vanished flight which originated from the Malaysian capital Kuala Lumpur and lost contact en route to Beijing when it was cruising over Vietnamese airspace.

Nearly two-thirds of the 227 passengers on board the airliner were Chinese nationals.

"We have a responsibility to demand and urge the Malaysian side to step up search efforts, start an investigation as soon as possible and provide relevant information to China correctly and in a timely manner," said Chinese foreign ministry spokesperson Qin Gang.

"The missing plane belongs to the Malaysian airline, so it is reasonable that the Malaysian side takes the major responsibility for the search and rescue work."

Search operation

Dozens of ships and jets from several nations have been scouring the South China Sea for the past four days in vain.

Malaysian authorities have pledged to boost their search efforts in the coming hours.

"Unfortunately we have not found anything that appears to be objects from the aircraft, let alone the aircraft. As far as we are concerned, we have to find the aircraft, we have to find a piece of the aircraft if possible," head of Malaysia's Civil Aviation Authority, Azharuddin Abdul Rahman, told reporters.