MELBOURNE, Australia (AFP) - - A Qantas jet was forced to make an emergency landing at Adelaide airport Monday night after a door opened during a flight to Melbourne, a report said.

The Herald Sun newspaper quoted unnamed passengers as saying a door opened causing "chaos" in the cabin of the Boeing 737-800, which left Adelaide at 6:08pm (0808 GMT) and returned safely 37 minutes later.

But airline sources said only the door covering the wheel bay was not closed properly after take-off, the Herald Sun said.

A Qantas spokesperson refused to comment beyond confirming an incident had occurred on the flight, the newspaper reported, and calls to the airline later were not immediately returned.

The incident came three days after a Qantas Boeing 747-400 en route to Melbourne from Hong Kong was forced to make an emergency landing in Manila after a hole was ripped in its fuselage.

Investigators are focusing on the possible explosion of an emergency oxygen cylinder as the cause of the mid-air drama.

The plane, which had originated in London and was carrying 365 passengers and crew, plunged 6,000 metres (20,000 feet) before stabilising, then made an emergency landing in Manila.