The Australian government imposed a requirement on Monday that its airlines have two crew members in the cockpit at all times as a safety precaution following the Germanwings crash that killed 150 passengers and crew last week.

Australian Deputy Prime Minister Warren Truss said the mandatory "rule of two", which means a flight attendant must stand in whenever the pilot or co-pilot leaves the cockpit, would be effective immediately.

The rule will apply to all domestic and international flights by Australian operators carrying 50 or more passengers. The carriers include Qantas, Jetstar, Virgin Australia and Tigerair Australia.

"The airlines will be acting immediately to implement this change and we'd expect to see this policy in place within hours on our major airlines," Truss told reporters in Melbourne.

US airlines had the rule in place before the Germanwings crash, in which investigators believe the co-pilot locked out the captain when he visited the toilet and deliberately steered the plane into the French Alps.

Regulators in Canada and New Zealand introduced the rule within 24 hours of the Germanwings crash and the European aviation authority has also recommended the change.

Truss consulted with the airlines to ensure the change would not open up other potential safety concerns. He said the government and the aviation regulator, the Civil Aviation Safety Authority (CASA), were considering other changes to improve cockpit security.

Mental illness is believed to have played a part in the Germanwings crash. German authorities said they had found torn-up sick notes showing that co-pilot Andreas Lubitz, 27, was suffering from an illness that should have grounded him on the day of the crash.

Australian pilots are subject to annual medical reviews, including a psychiatric assessment.

"There is a need to balance the fact that people with proper treatment can recover from mental illness and be able to undertake normal careers with the critical priority of ensuring that aircraft are always safe," Truss said. - Reuters