An explosion that ripped a hole in a jumbo jet may have been caused by an oxygen bottle.

Australian airline Qantas has been ordered to check all oxygen cylinders on its Boeing 747s after a warning from accident investigators.

A Qantas 747 was forced to make an emergency landing at Manila after part of the undercarriage was torn off, triggering a loss in cabin pressure during a flight from Hong Kong to Melbourne.

Passengers reported hearing a loud bang before the aircraft rapidly lost height, and said the plane had a hole the size of a car on the right of its undercarriage when it landed in the Philippine capital.

Australia's Civil Aviation Authority (CASA) said Qantas has agreed to inspect oxygen bottles on its fleet of 30 747s.

CASA spokesman Peter Gibson said: "There are two cylinders located pretty much exactly where that hole appeared."

He added: "We do know there were two oxygen bottles in that area, we do know they're a main focus of the investigation, and we think it's prudent to put safety first, to get inspections done now rather than wait any longer."

Mr Gibson also said investigators would look into reports that oxygen masks on the plane were in poor shape and some failed to work properly during the emergency.

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