SYDNEY - AUSTRALIAN airline Qantas said on Friday it was checking oxygen cylinders in all its jumbo jets after a mid-air scare forced a 747 to make an emergency landing in Manila with a huge hole in its fuselage.

An exploding oxygen cylinder has emerged as the most likely cause of the emergency, when a blast punched a three metre hole in the side of the plane as it was flying from Hong Kong to Melbourne on July 28.

Australian investigators have confirmed that fragments from a metal cylinder flew into the jet's passenger cabin mid-flight with enough force to shear off a door lever, although they have not yet said what caused the hole in the plane.

A Qantas spokesman said oxygen cylinders in all the airline's 747s were being checked.

'It has been a process for a few days ... we do the checks as the aircraft arrive back in Australia,' a Qantas spokesman said.

'We will complete checks of the cabin emergency oxygen bottles across out Boeing 747 fleet tonight.'

The passenger cabin depressurised during the emergency and oxygen masks deployed from the ceiling as the plane made a 6,000 metres descent and diverted to Manila.

Passengers described the ordeal as 'absolutely terrifying'. -- AFP