The Boeing 747 carrying more than 300 passengers and crew dived 20,000 feet after a panel came off in-flight, creating a 7-by-9 foot hole in the fuselage, The Times of London reported. The plane was diverted to Manila to land after it had taken off from a stop in Hong Kong.

"It's possible there was some kind of explosive device in the suitcases. There's a hole where there shouldn't be," David Learmount, safety editor of Flight International Magazine.

However, he stressed, other possible causes could be physical damage or a corrosive that weakened the hull. Learmount said the hole had exposed luggage usually stored inside containers in the hold.

"It's interesting to see them -- how else could that be if not an explosion?," he told the Times. "Bags are moved about quite roughly in the hold... . If damage was done to the fuselage over a period of time a crack could have developed ... weakening to the point where it was blown out."

While not finding any immediate indication of terrorism, investigators said they will look for any evidence of a bomb, as well as other reasons.

"It should become apparent fairly quickly if something exploded or something broke," said Kieran Daly, editor of the Internet news service Air Transport Intelligence.