Air safety investigators were Saturday searching for clues as to what caused a dramatic mid-air rupture which left a gaping hole in the fuselage of a Qantas plane carrying more than 300 passengers.
  
Experts were working on the theory that an explosion in the luggage hold or a broken panel caused a fuselage break in the 747 that made an emergency landing in Manila Friday, a source close to the investigation said.
  
Regardless of the cause, the source said the 365 passengers and crew on the flight from Hong Kong to Melbourne were lucky to be alive after a three metre (10 foot) hole was punched in the jet's belly at 29,000 feet (8,800 metres).
  
"They were very lucky," the source, who asked not to be identified, told AFP.
  
"While it is too early to say what actually caused the hole, we will be looking at two possibilities ... something exploded in one of the bags or a panel came loose on the fuselage" the source told AFP.
  
The source said the explosion might have been caused by a pressurised container inside a piece of luggage, saying a bomb was unlikely.
  
Qantas officials and experts from the Australian Transport Safety Bureau are working with Philippines authorities on the investigation.
  
Meanwhile, the plane's passengers completed their interrupted journey to Australia, staging emotional reunions with relatives and recalling how they thought they would die as the plane plunged towards the South China Sea.
  
Many were still shaken by the ordeal which saw the aircraft plunge 6,000 metres (20,000 feet) in an emergency descent before stabilising.
  
As oxygen masks deployed from the ceiling and debris swirled around the cabin, passenger Steve Winchester thought he was going to die.
  
"Everyone was just thinking to themselves 'Oh I think this is it'," he told reporters.
  
"I heard someone scream. People were just looking at each other in sheer terror."
  
Melbourne man David Saunders said he hugged his girlfriend and put his passport in his pocket so his body could be more easily identified if the plane crashed into the sea.
  
"I heard an enormous explosion, things went quiet, the cabin instantly lost pressure and the plane just started to dive. I thought we were going down into the sea," he said.
  
The plane involved in the incident is 17 years old and Sydney's Daily Telegraph reported that engineers discovered a large amount of corrosion in it during a major refurbishment earlier this year.
  
Under the front page headline "Rust Bucket", the newspaper said the jet received a new interior at Melbourne's Avalon airport in March and said aviation sources had told it engineers had found a lot of corrosion.
  
The plane took off from London and was heading to Melbourne after a stopover in Hong Kong when the incident occurred.
  
Qantas Airways boasts of its safety record, having never lost a jet to an accident.