A machinery operator has been treated and released from hospital with burns after a large fire broke out at the Ports of Auckland.

Plumes of black smoke could be seen billowing across the city, including the North Shore, from the blaze this morning.

The blaze had broken out near railway lines alongside Quay St in a reach stacker, a vehicle used to lift and move cargo containers, a Fire Emergency New Zealand spokesman said.

The operator suffered burns and was taken to hospital.

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Ports spokesman Matt Ball said at 1pm the male driver of the stacker had been treated for minor burns to a hand and released from hospital.

Four fire trucks attended the fire.

The blaze was limited to the one piece of machinery, Ball said.

Eyewitness Li Li said he and his family saw the inferno from across the road.

"At the time it was very dangerous," Li said.

"The fire got bigger and bigger."

Within about 10 minutes firefighters arrived, Li said.

"They were very brave."

The reach stacker is still holding on to one of the nearby containers. At least a dozen firefighters are still at the scene on the rail grid alongside Quay St.

Firefighters were hosing down the inside of the container still attached to the charred reach stacker at 11am.

The cab of the loader usually has glass protecting the driver but it appears to have been blown out in the blaze, nearby workers said.

Some reported hearing a "loud bang" as the fire broke out.

Because there was diesel involved, the fire created large clouds of black smoke, the spokesman said. The fire has now been brought under control.

Witness Sarah Bowman said she saw a thick plume of smoke rising from the Ports of Auckland about 20 minutes ago from her third-floor office on St George's Bay Rd.

A video sent to the Herald shows a vehicle fully ablaze near several containers at the port as firefighters work to bring the fire under control.