The fire was reported about 6.30pm yesterday in a forest owned by company Earnslaw One at Tangimoana, southwest of Bulls, Earnslaw One duty fire officer Tony Groome said.

It was next to a Department of Conservation (DOC) reserve.

Between 70 and 100 firefighters had been sent to the fire from volunteer brigades in the surrounding area, along with firefighters from Palmerston North, and crews from DOC, the Manawatu District Council and Earnslaw One.

A helicopter with a monsoon bucket dumped water on the fire for up to 2½ hours, as firefighters on the ground worked on the blaze with hoses and hand tools, Mr Groome said.

The fire crews were stood down about midnight, with checks continuing at the scene throughout today.

It was estimated an area of about 4ha had been affected by the fire, but it had the potential, had the area been dryer and the wind stronger to be a much larger fire, he said.