The Australian Transport Safety Bureau said in an official statement that it was sending four investigators to Manila to assist local authorities with the investigation.
An initial report by the airport authority, quoting pilot John Francis Bartels, said that the passenger jet suffered an "explosive decompression". While Australia's air-safety investigator said an initial investigation suggested "a section of the fuselage separated".
Qantas flight QF30, which took off from Hong Kong at 1:00 GMT, had been due to arrive in Melbourne at 11:45 GMT, according to the Qantas website, but after being forced to land in teh Philippines capital passengers were taken to a hotel.
"There was a terrific boom, and bits of wood and debris just flew forward into first class and the oxygen masks dropped down," June Kane, a passenger from Melbourne, said.
|An initial investigation said a section of fuselage separated [AFP]
"We were told that one of the rear doors, a hole had blown into it, but I've since looked at the plane and there's a gigantic gaping hole in the plane.
"It was absolutely terrifying, but I have to say everyone was very calm," she said, speaking from the Philippine capital.
Phil Rescall, a 40-year-old man from England travelling to Australia for work, said: "The shock came when many got off the plane and saw the hole.
"You see the hole and you realise we were very lucky," he said.
Geoff Dixon, Qantas chief executive officer, said the flight crew praised the pilots and the rest of the 19-person crew for how they handled the incident.
"This was a highly unusual situation and our crew responded with the professionalism that Qantas is known for," he said.
Australia's largest domestic and international airline has a good safety record and has never lost a passenger jet to an accident.