Nelson police said they were notified but the plane, en route from Christchurch to Hamilton with 58 people on board, had landed safely.
The Air New Zealand ATR72-600 sits on the Nelson Airport tarmac following an emergency landing on Tuesday. Police said the plane was diverted because of a problem in the cockpit. There were no further details about the nature of the problem.
Nelson Fire Station officer Paul Marshall said the plane made an emergency landing in Nelson after the pilot noticed a bit of smoke in the cockpit.
"They have landed as a bit of a precaution," he said. "Everybody is off [the plane] and happy."
The Nelson Fire Service responded to the incident at 3pm and were stood down once the plane landed safely and it was now being dealt with by airport staff, he said.
"We are just on local standby, it wasn't a full emergency," he said.
Graham Bell was on the flight with wife Margaret when they smelt what seemed to be smoke coming through the overhead air vents.
"We were just flying along nicely and all of a sudden there was just a smell of burning coming through the air vents. The pilot said we're going to have turn around and go to Nelson instead of Hamilton," Graham said. "You could smell it. It was quite strong," Margaret said.
Graham said there was a "wee bit of turbulence" on the way down, but the landing was smooth.
"We're just finding out if they're going to fix that one or give us a new plane, so how long we're going to be here, I don't know."
Trevor Johns, who was flying home to Hamilton, said the burning smell was "putrid" like "burning fur".
"Just started getting a bit distressed wondering what's that smell, what's going on, what's happening? The captain just pulled pin, eh," he said.
"The mood was heavy, mate. People were worried."
He said the pilot said the plane had electrical issues and they needed to initiate an emergency landing.
Passenger Pete Caldwell said the mood on the plane was "pretty relaxed".
"They seemed to have everything under control pretty well."
However, he was surprised that no one from Air New Zealand had met the passengers at the airport to explain what had happened and what their options were.
Nelson Airport chief executive Rob Evans said the aircraft was diverted and that it was a normal procedure and not unusual.
Police cordons were in place around the airport as a pre-caution, but were lifted by 3.30pm.