At least three homes were evacuated after multiple suspicious fires in Piha overnight.

Photo: Alistair Wilkinson / @AlistairWilk

The largest, a scrub fire, started in multiple locations and burnt through at least 7ha of scrub, and was 1km away from at least 20 houses in the beachside town west of Auckland.

Fire Service shift commander Jaron Phillips said three of the houses were evacuated overnight and about a dozen others were placed on standby.

All occupants have since been allowed to return.

Mr Phillips said they had initially been called out to a fish and chip shop about 1.30am. It was ablaze when the first of five crews arrived, he said.

The Fire Service then spotted the scrub fire just before 2am near 'The Gap' or Blue Pools.

Shift commander Jaron Phillips said 17 fire engines and a helicopter were already fighting the main blaze, and more crews were on their way.

"The second fire, which is the larger one, is burning at The Gap and ground crews are continuing to work on those flanks attempting to contain that fire.

"One helicopter is on scene now working with a monsoon bucket and a second has just been dispatched."

Mr Phillips said another fire at the Tasman Lookout had been contained.

Photo: Alistair Wilkinson / @AlistairWilk

Adey's Place fish and chip shop was significantly damaged and was being guarded by police, the Fire Service said, and there have been a spate of suspicious fires in the town in recent weeks.

A woman who worked the fish and chip shop, Kaya Prebble, said she was woken by the sirens and saw the shop engulfed in flames.

"I went outside onto my balcony and I could see the flames that were up on the hill from the big scrub fires and I also saw flames coming from down here. I didn't know if it was Adey's [fish and chip shop] or the surf club. But I just jumped in my car and raced straight down," Ms Prebble said.

"It broke my heart when I saw it was Adey's. It's really hard because it's such a great little shop - it's an iconic shop - that's been here for years and years."

She said the owner, Adey, was on a week-long holiday in Fiji, set to return home today.

"My heart just broke for him, I just had a little cry and I sat there. And I sat there for him because I know if he was here he wouldn't leave."

Photo: RNZ / Sarah Robson

"You're happy that everyone is safe but it's still hard because it's somebody's business, people's jobs ... it's one of our places."

Ms Prebble said the firefighters were amazing. After fighting the blaze at Adey's they went up the hill to the scrub fires which wasn't the easiest spot to get to, she said.

"I just saw the flashlights of [the fire fighters] having to walk up the track in their suits after fighting one fire, going to fight the other two."

Ms Prebble said everyone was "already on edge" because of the recent spate of fires in the area.

"We're like a family out here and we don't want anyone to be affected by something so stupid as arson. Everybody just wants these people to be caught," she said.

"It's a hard time for us. It's a really sad time for everyone in Piha at the moment."

Photo: RNZ / Sarah Robson

The Waitemata Criminal Investigations Branch would be investigating the fires, and asked the public for sightings of anyone in the area behaving suspiciously before the fires.

Detective Inspector John Sutton said scene guards were situated at Adey's Place near Piha Surf Club.

"We are aware that there have been a number of reports of suspicious fires in the area this week and are focussed on apprehending those responsible," Mr Sutton said.

"We are treating this fire as unexplained and ask residents to be vigilant about reporting any suspicious behaviour.

"Police will be increasing patrols in the Piha area throughout today and overnight.

Car fire on motorway near Mt Albert

Meanwhile, police said a car had been on fire on Auckland's Northwestern Motorway.

The car hit a barrier about 200m before the Great North Road off ramp.

Police and firefighters were at the scene.