A bush fire in Auckland's north is threatening nearby houses as fire crews work to get it under control.

The fire in Selman Rd, Dairy Flat started up just before 1pm on Sunday.

The fire has spread through bushland over "four or five hectares", says Fire and Emergency New Zealand shift manager Colin Underdown.

He says getting the fire under control is a "work in progress".

"Right now we're protecting houses as the wind is blowing the fire towards them," Underdown says.

There are three helicopters as well as a number of fire trucks on the scene.

Underdown says the heat and strong winds are not aiding the fire fighting efforts.