Fire crews were kept busy throughout Auckland overnight as they battled two large blazes.

They were first called out just before 11pm to a two-storey warehouse fire on Hannigan Road in St Johns, northern fire communications shift manager Tania Matthews said.

About 20 appliances were called to the 40m by 40m building, which was "fully involved'' when fire crews arrived.

Crews have stayed at the scene through the night and were still there dampening down hotspots, Ms Matthews said.

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Fire inspectors would arrive at the scene this morning to work out the cause of the fire.

In the second incident, crews were called to a large boat fire at a boatyard on Akatea Road in Glendene, about 11.40pm, Ms Matthews said.

Twelve appliances were needed to extinguish the blaze on the 10m boat.

At one point the fire was endangering a nearby boat, she said.

That blaze was not considered suspicious.

Nobody was injured in either fire, Ms Matthews said.