SYDNEY, April 16, 2009 (AFP) - A Qantas airliner was grounded after four snakes went missing from the cargo hold on a passenger flight from Alice Springs to Melbourne, officials said Thursday.

Twelve baby pythons were packed on the Boeing 737-800 in the outback town on Tuesday, but when it arrived in Australia's second biggest city there were only eight, Qantas said in a statement.

Corporate manager David Epstein told public radio the snakes' escape was a mystery because the consignment had been properly packaged in a tied calico bag inside a Styrofoam box with air holes punched in it.

"Our people called in a reptile expert and there was a suggestion that some of the baby pythons had eaten the other pythons because apparently it is not uncommon for baby pythons to eat each other," he said.

Qantas staff then weighed the remaining snakes to determine if they were heavier, but they were not.

"The only conclusion we could draw was four of them had broken free of the packaging," Epstein said.

"We thought the best thing to do was to call in a wildlife expert and determine if they're endangered or not.

"They're not endangered, so a decision was made to take the plane out of service and fumigate it, so if these snakes ever turn up on one of our aircraft, they will be very much dead snakes," he said.

The Stimson's pythons, which the Qantas statement was at pains to point out were "non-venomous infants" about 15 centimetres (six inches) long, can grow up to a metre.