Key Points:

Passenger laptop computers are now being investigated as a possible cause of the Qantas mid-air emergency off Western Australia on Tuesday.

The Airbus A330-300, with 303 passengers and a crew of 10, experienced what the airline described as a "sudden change in altitude" north of its destination on Tuesday.

The mid-air incident resulted in injuries to 74 people, with 51 of them treated by three hospitals in Perth for fractures, lacerations and suspected spinal injuries when the flight bound from Singapore to Perth had a dramatic drop in altitude that hurled passengers around the cabin.

In July, a passenger clicking on a wireless mouse mid-flight was blamed for causing a Qantas jet to be thrown off course, according to the Australian Transport Safety Bureau's monthly report.

Safety investigators will now ask passengers if they were using any electronic equipment at the time of this latest incident.

"Certainly in our discussions with passengers that is exactly the sort of question we will be asking - 'Were you using a computer?'," The Courier Mail quoted an Australian Transport Safety Bureau (ATSB) spokesman as saying.

The ATSB said the pilots received messages about "some irregularity with the aircraft's elevator control system", before the plane climbed 300 feet and then nosedived.

"The aircraft is then reported to have abruptly pitched nose down," the director of aviation safety investigation Julian Walsh said.

The plane was forced to make an emergency landing at Learmonth air force base near Exmouth in WA.