UPDATED 4.38pm A fire in a central Auckland high rise has been contained.

The blaze is believed to have started while demolition contractors were working in the plant room on top of the 19-storey building.

Fire communications shift manager Dallas Ramsay said about 50 firefighters were called to the scene at the corner of Mayoral Drive and Queen Street, just after 3pm.

She said the fire itself is contained to a large metal box on top of the building.

An eyewitness, John, told Kerre McIvor and Mark Dye he's never seen so much smoke.

"It's quite spectacular, just the visual impact of this billowing smoke. It's quite daunting really."

@RPamatatau On mayoral Drive next to AUT International Centre Police and multiple fire trucks on scene pic.twitter.com/fNMvgzPgy2

— Grace Mitchell-Ellis (@GraceMitchellis) May 18, 2017

The building is next to AUT's International Centre though AUT has confirmed the fire is not at one of their buildings.

Confirming downtown Auckland fire is NOT at AUT. ^^AS

— AUT (@AUTuni) May 18, 2017

Smoke from the fire is stretching as far as Albert Park.

The 19-storey building is owned by Russell Property Group, which is planning to convert it into a 250-room hotel.

Russell Property Group owner Brett Russell said a demolition subcontractor had been working in the plant room on top of the roof when the fire started.

“From what I believe the demolition guys were cutting something on top of the roof and what they were cutting had a small explosion.

“We’re not sure what caused it, they’re investigating it now. The fire brigade’s there and everybody’s safe,” he said.

Strong winds are probably making the fire look worse than it is, he said.

“From what I’ve been told, it’s contained on the roof at the plant room. Nobody was hurt, and they think it’s under control.”

The hotel is still under construction and has no occupants. The company’s partners Dominion Constructors are managing the build but their staff were not involved in the incident.