More than 40 people were injured when the plane was forced to land after the pilot reported a sudden change in altitude Wednesday, the Australian Broadcasting Corp. reported.

The pilot of the A-330-300 issued a mayday call after the in-flight incident in Western Australia. The plane was traveling from Singapore to Perth when it was forced to land at Learmonth Airport near Exmouth, the Australian broadcaster said.

Qantas Regional Manager Ian Gay said the cause of the sudden altitude change was unknown.

"In terms of what happened, we'll be investigating all sorts of possibilities, clear air turbulence perhaps," Gay told ABC. "But we'll have to be looking at all of those, we don't have any details at the moment."