A firefighter suffered burns and a person who escaped a burning home was treated for smoke inhalation in a spate of fires across New Zealand overnight.

Three homes have been damaged in blazes in Auckland and Invercargill and a commercial property has been gutted in Murupara.

At least two of the fires have been deemed suspicious and firefighters credit working smoke alarms for saving lives.

Fire crews are still at a blaze on Auckland's North Shore after fire broke out about 1.45am on the outside walls of a double-storeyed home.

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Fire and Emergency northern shift manager Jaron Phillips said a person inside the Torbay house escaped the blaze but suffered smoke inhalation.

Fire crews were still at the property and specialist fire investigators are expected at first light to determine what caused the destructive blaze.

Just after midnight an unoccupied commercial building in Murupara was engulfed by a suspicious fire and a firefighter was treated for burns.

Phillips said the fire tore through the building at the rear of the town's shopping centre and six crews battled the inferno.

A firefighter was treated at the scene by St John Ambulance officers.

Police and fire safety officers would investigate the cause of the fire this morning. It was being treated as an arson, he said.

Residents of two Invercargill homes had lucky escapes after fire broke out within hours of each other.

Fire crews were called to a Beaumont St property just after 10.15pm after fire broke out in the roof. The person inside managed to escape unharmed.

A Fire and Emergency spokesman said less than three hours later a garage attached to a home in Tweed St, Newfield, where people were sleeping, caught alight.

By the time fire crews arrived the family had got out to safety thanks to working smoke alarms, said the spokesman.

The fire was thought to have been sparked by an electrical fault and not deemed suspicious.