Emergency services were scrambled after an Air New Zealand flight from Sydney carrying 99 passengers and eight crew was diverted to land at Auckland late last night.

A Fire Service spokesman said five trucks were sent to back up two airport-based crews when the Airbus 320, originally bound for Wellington, touched down at 11.10pm.

Police and ambulance staff were also on alert as the flight approached New Zealand.

"We always work on a worst case scenario," said one senior police officer. "The ground crews are all aware and are taking whatever precautions they need to take."

The flight was diverted after pilots were alerted to a possible problem with the hydraulic system and nose wheel. The plane landed 10 minutes earlier than its scheduled arrival in the capital.

An Air NZ spokeswoman said: "NZ144 Sydney to Wellington was diverted to Auckland because of a warning light coming on. It is with engineering services at the moment."

The diversion left the passengers stranded in Auckland overnight. They were put up in an airport hotel and were scheduled to arrive at Wellington at 2.30pm today.

Lower Hutt's John Standish said the captain announced an undercarriage problem about halfway through the flight.

Passengers remained calm - but there was frustration at the long wait in Auckland.

Holly Griffiths, 21, of Sydney, said passengers were "freaked out" when told there would be fire engines waiting on the plane's arrival.

"The landing was fine. They made a whole lot of fuss about nothing."

And she said it was the second Air NZ flight she had travelled on that had suffered problems: "I'm never flying Air NZ again."

Another passenger criticised the lack of Air NZ staff at Auckland airport to tell them what was going on.

There was no one available to comment at the Civil Aviation Authority.

It's at least the fourth mechanical scare on an Air NZ flight this year.

Passengers on a Boeing 767-300 flying from Sydney to Auckland on February 2 were told to prepare for an emergency landing because of a problem with the aircraft's flaps.

A Boeing 777 was forced to abort its takeoff from Narita airport in Japan on January 31 when the pilot discovered a problem with the auto thrust control. Twelve tyres burst.

A flight from Auckland to Cairns was diverted on January 10 because of a cracked windscreen.