A passenger aboard an Air New Zealand aircraft described how a stewardess screamed "head down, stay down" as the plane lurched into an emergency landing.

Passenger Gary Evans said the atmosphere on the plane changed suddenly from one of calm to high tension.

"It was just a bit shocking when all of a sudden it went from all so calm, then all of a sudden [the stewardess] started screaming 'head down, stay down'," Mr Evans said.

"I'm just really pleased to be on the ground. I need a drink that's for sure."

The Q300 aircraft, operated by Air Nelson, a subsidiary of Air New Zealand, was flying from Hamilton to Wellington when it encountered problems with its landing gear.

After circling over Wellington and trying unsuccessfully to lower the nose wheel, the plane was diverted to Blenheim Airport about 2pm. Emergency services were on standby as the plane circled over Blenheim.

Passenger Colin Hayman said the crew let the passengers know there was a landing gear problem over Wellington Harbour and "people went reasonably quiet".

Once over Blenheim, the passengers were told they would have to go in and land. They were told to follow the instructions of the stewardess "who was handling the whole situation on her own".

"There was definitely nervousness," Mr Hayman said. "There was repeated instruction to keep your head down and stay down, and that went on, I guess, for a full minute before landing. They weren't there to muck around."

When it came, the landing without the nose wheel was "remarkably smooth". It was followed by a round of applause from the passengers.

Mr Hayman and Mr Evans praised the handling of the incident by the crew, and the "great job" by the pilot.

The passengers were last night offered accommodation or road transport to Nelson for another flight on to Wellington.