The plane was flying from Hong Kong to Melbourne, the last leg of a trip from London, and was at 29,000 feet at the time of the incident Friday. The pilot got the plane to 10,000 feet, where passengers could breathe without emergency oxygen, and then made an emergency landing in Manila in the Philippines.

The incident is being investigated by the Australian Transport Safety Bureau, The Times of London reported. The newspaper cited a source close to the Civil Aviation Safety Authority.

"It is looking extremely likely that one or more of the oxygen tanks exploded," the source said. "It's never happened before so nobody knows what caused it. It could be as simple as some cargo shifting and smashing into it, which shouldn't be able to happen."

The newspaper said investigators found debris from two oxygen tanks that provide an emergency supply for the pilots scattered in the cargo hold.

No one was injured in the incident, in which passengers heard a loud bang followed by the opening of a gaping hole in the side of the Boeing 747 jet carrying 346 passengers.

An investigative team from Boeing Co., manufacturer of the 747-400 jumbo jet, also was in the Philippines to inspect the aircraft, the newspaper said.