A fire investigator says a fire that destroyed dozens of cars in a Whangārei Hospital carpark is a timely reminder of the danger of hot exhausts.

The fire broke out just after 2pm on Tuesday in the staff carpark between the hospital campus and Raumanga Stream.

The blaze started with just one vehicle but quickly spread down the rows of cars, sending flames and thick, potentially toxic, smoke into the air.

One witness reported hearing small explosions as fire spread through the busy carpark.

Fire investigator Jason Goffin said it was most likely an accidental fire, from a hot exhaust pipe igniting the grass in the centre of the carpark.

“It’s looking likely that it’s definitely the exhaust on the grass,” he said.

“It’s a timely reminder that hot exhausts can ignite dry vegetation material.”

Goffin said people need to be aware of the problem and avoid long-dry grass if they have a hot exhaust.

On Wednesday, insurance assessors were getting involved, he said.

Health New Zealand thanked Fire and Emergency and police for their swift and effective response to the fire.

Te Tai Tokerau group director of operations Alex Pimm said the organisation was supporting impacted staff, including offering alternative transport home on Tuesday evening.

A section of the carpark will remain closed but the rest reopened late Tuesday.

Clinical services at the hospital continued throughout the incident, Pimm said.

Denise Piper is a news reporter for the Northern Advocate, focusing on health and business. She has more than 20 years in journalism and is passionate about covering stories that make a difference.