If you hear an unusual message over the PA system to not fetch your mobile phone mid-fight if you drop it under your seat during your flight. the reason is simple: they pose a fire hazard.

Airline passengers have been left befuddled by announcements warning them "not, repeat not, to try find it themselves" if accidentally devices get wedged between reclining seats. The lithium-ion batteries in smartphones can catch fire if they become damaged or crushed.

On a Qantas flight from Sydney to Dallas-Fort Worth in May cabin crew were alerted to the "presence of smoke in the cabin".

The Australian Transit Safety Bureau (ATSB), found the source of the smoke was traced to seat 19F, in business class – to "a crushed personal electronic device [a phone] wedged tightly in the seat mechanism".

"We're asking people to keep track of their phone in their seat, and if they do lose it down the side, to let a crew member know and to not move their seat," a Qantas spokesperson told the Telegraph.

"We find this tends to be more of an issue on longer flights and on our Business Class skybeds, where people might have their phone next to them as they relax and it slips down the side of the chair.

"Our crew are trained to deal with this scenario and they've done a great job on the odd occasion where we've had a phone break and start to smoulder. But obviously, we'd much prefer if we could avoid this happening altogether."

Since July, other airlines such as British Airways (BA) and Virgin Atlantic flights have made similar warnings to passengers following guidance issued by the Civil Aviation Authority (CAA).