Malaysia has formally declared missing flight MH370 an accident and its passengers and crew presumed dead.

Civil aviation chief Azharuddin Abdul Rahman says the official decision that the plane's disappearance on March 8 was an accident would allow families to move on and receive payments from the airlines.

Some relatives accuse the Malaysian government and its flag carrier of a chaotic and bungled response to the plane's initial diversion, which allowed the jet to disappear, and a subsequent cover-up.

Kuala Lumpur and Malaysia Airlines strenuously deny these charges.

MH370 vanished en route from Kuala Lumpur to Beijing in what remains one of history's great aviation mysteries.