Air safety investigators have released a preliminary report into a Qantas mid-air emergency when an oxygen tank exploded shortly after a flight left Hong Kong for Melbourne in July.

The report by the Australian Transport and Safety Bureau contained a detailed account of how one of seven passenger oxygen cylinders failed and then exploded into the aircraft hold.

It ruptured the fuselage, puncturing the cabin floor and entering the cabin before falling to the cabin floor and exiting the aircraft through the ruptured fuselage.

The Bureau says investigations are continuing into the functioning of the cabin oxygen masks and into the design and manufacture of the failed oxygen cylinder.

The survey of all passengers is also being conducted.

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