A Jetstar flight is being investigated for flying too low on approach into Queenstown in New Zealand.

The Australian Transport Safety Bureau (ATSB) is investigating, saying the two-pilot crew of the Airbus 320 had an incorrect descent profile selected and descended below the minimum safe altitude on the morning flight from Auckland to Queenstown on July 16.

Jetstar said although the flight landed safely in clear conditions, the airline was taking the incident very seriously and was working with the bureau.

''The pilots reported that on approach an incorrect autopilot setting resulted in the aircraft going off its pre-determined track.''

The aircraft dropped to 1920m for a short time when it should have been flying at 2225m.

''This never put the aircraft in danger and the incident didn't trigger any cockpit alerts. The pilots realised the error and corrected it promptly,'' a Jetstar spokesman said.

The two pilots, who had a combined total of 23,000 hours' experience and had been flying to and from Queenstown for the past two years without incident, reported the incident to Jetstar and to the Civil Aviation Safety Authority (CASA), Australia's equivalent of the New Zealand Civil Aviation Authority.

Under a treaty between Australia and New Zealand, CASA was viewed as the air safety regulatory body for Jetstar.