An investigation is underway into how a smartphone battery sparked a fire on a Qantas flight to Los Angeles.

The Australian Transport Safety Bureau is investigating the incident on June 21, on a Qantas 747 flying from Sydney to LA.

Six-and-a-half hours into the 13-hour flight a passenger's smartphone slipped between the seats and was crushed when the reclining mechanism was used.

The battery in the crushed phone then erupted into flames. Crew used a fire extinguisher to put out the blaze and the flight continued on to Los Angeles.

Advertisement

The ATSB confirmed the incident, and said it would seek information from Qantas as part of its investigation.

Last year Qantas and other Australian airlines banned the carriage of lithium-ion batteries in cargo holds after they were found to pose an unacceptable risk of fire.

It followed tests by the US Federal Aviation Administration showing an overheating battery could cause other batteries nearby to short-circuit in a chain-reaction.

The subsequent ignition could be enough to cause an explosion strong enough to blow the door off a cargo container, resulting in fire.

Such a scenario is considered one possible cause of the MH370 mystery.

The Malaysia Airlines' Boeing 777 was carrying 200kg of lithium ion batteries in its cargo hold when it took off from Kuala Lumpur with 239 people on board.

Shortly after the plane's still unexplained disappearance, Malaysia Airlines imposed a ban on the bulk carriage of lithium-ion batteries.

The ATSB investigation into the June 21 incident is expected to take several months.

A statement is being sought from Qantas.