"In the vicinity of the damage, we are missing one cylinder. The areas around the damage will be inspected. We're obviously looking for evidence on where that cylinder may have gone," he said.

Bomb tests 'negative'

Blyth also said tests for bomb residue were negative. Philippine bomb-sniffing dogs went through the aircraft, particularly the cargo hold and the passenger baggage, and found no indication of explosives.

Australia's Civil Aviation Safety Authority said that Qantas had been ordered to urgently inspect every oxygen bottle aboard its fleet of 30 Boeing 747s.

Peter Gibson, spokesman for the Civil Aviation Safety Authority, said that inspection would take several days. He also said that bottles located near the hole contained emergency oxygen for the flight deck.

The passengers on Flight QF 30 had just been served a meal after a stopover in Hong Kong when they heard a loud bang, then their ears popped as air rushed out of the 9ft hole in the aircraft's side.

Oxygen masks dropped from the ceiling as the jet descended rapidly and debris flew through the cabin from a hole that suddenly appeared in the floor.

There were no injuries among the passengers and crew.

Four specialists from the Australian Transport Safety Bureau inspected the aircraft on Saturday and were to continue through the weekend.

Boeing and the US National Transportation Safety Board were also sending specialists to assist.

Rust ruled out

Gibson has said speculation that rust contributed to the accident could be discounted.

Passengers of Qantas747 have complained of faulty emergency equipment [AFP]
"It's clearly an extremely rare and unusual event that a hole opens up in the fuselage," he said in Australia.

"I know there's a number of theories around, but they're just that at this stage, they're just theories. We don't have the solid facts."

Qantas boasts a strong safety record and has never lost a jet to an accident. The last crash of a smaller airline was in 1951.

Meanwhile, some passengers told Australian media that their oxygen masks failed to work properly during the crisis, leading some to nearly pass out.

Other passengers, while applauding the pilot and crew's performance, told of having to share oxygen masks between three people because of faulty or broken emergency equipment.