NZDF plane that Jacinda Ardern used to travel to Australia breaks down

The New Zealand Defence Force plane that the Prime Minister used to travel to Australia has broken down.

Jacinda Ardern was meant to fly back to New Zealand tonight, but issues with the aircraft have kept it grounded.

It is unclear at this stage if Ardern will be flying to New Zealand commercially, or remaining in Australia.

Details around why the plane is grounded are unknown at this stage.

A day before the trip, the plane was encountering issues.

A Defence Force spokesman said the aircraft's air data computer failed during pre-flight checks. The computer was a essential part of its flight management system.

A replacement part was being flown to Australia and it was expected the repair would be made tomorrow.

Ardern has made alternative arrangements to return to New Zealand, the spokesman said.

The 757s have run into trouble before. National Prime Minister John Key was stranded in Townsville in 2016 when one of the 757s broke down during a stopover on the way to India - requiring a backup plane to be sent.

The NZDF's two 757s were acquired in 2003 at a cost of $221 million, which included the cost of modifications in 2007.

They are understood to have been 10 years old when they were bought.