Firefighters are battling steep terrain and limited water supplies to contain a large scrub fire near a pine forest in Dome Valley north of Auckland this afternoon.

Helicopters with monsoon buckets and fire retardant chemicals are helping to fight the blaze, which broke out yesterday on cutover forestry land next to a commercial pine forest, about 10km north of Warkworth.

The fire grew to 65ha yesterday and cooled overnight before growing to about 71ha this morning.

Principal rural fire officer Bryan Cartelle said the fire had not spread any further this afternoon but crews were battling challenging conditions including water supply issues and difficult terrain.

"It's steep terrain and it's cutover forestry so it's hard to work, but we've got some good operators in there and they're making some good headroads into it."

The priority was to get firebreaks in place to stop the fire from spreading any further.

Mr Cartelle said two helicopters were dropping water onto hotspots and two more helicopters were laying chemical retardant lines.

Diggers were working to cut firebreaks in the forest.

Mr Cartelle said a team of 43 volunteer rural firefighters, including some from Auckland and Whangarei, were fighting the fire and incident management personnel had been called in from Christchurch.

Several water tankers were also supporting the fire operation, which could delay residential water deliveries in the Matakana area.

It was hoped the tankers would be freed up as soon as possible.

No properties were in danger and smoke which had last night drifted over State Highway 1 was now minimal.

The cause of the blaze was not yet known but northern fire communications spokesman Jaron Phillips said it may have been started by skeet shooters seen in the area.

Last night a helicopter pilot fighting the fire needed medical treatment for ash in his eyes.

Mr Phillips said the pilot was flying one of three helicopters using monsoon buckets to fight the fire.

He was grounded so he could be treated by St John Ambulance officers.

The blaze is the second in the area within a week, after an area of gorse and grass caught fire in Tapora near Wellsford.

That fire has been contained but crews remained onsite.

Mr Cartelle said a complete fire ban across the Auckland region must be taken seriously because there was still an extreme fire danger.

- APNZ