Dunedin resident Alison, who asked to be only identified only by her first name, said she arrived at the Flagstaff Loop Track car park in Whare Flat Rd to walk her dogs about 7.20pm on Sunday.
She was waiting for a friend to join her when she saw white smoke coming from a car parked about 10m from her car.
She initially thought the car must have overheated.
A group of young people, who looked to be between 15 and their early 20s, were with the car, until they left in another vehicle.
The next time she looked, she saw flames and black smoke.
As the conditions were dry and windy, it did not take long for the fire to spread to nearby flax.
She was among several at the scene who called emergency services, Alison said.
One man’s van was 5m from the blaze.
Alison described the incident as "complete stupidity on behalf of those young people".
She was angry as she and others could have been killed had the fire got further out of control.
"It escalated very, very quickly," Alison said.
A Fire and Emergency New Zealand spokesman said the fire was considered suspicious.
Appliances from Mosgiel and Roslyn stations were initially sent.
A tanker from Portobello and another appliance from Mosgiel were also called.
The fire spread to bushes, grass and flax nearby and reached a size of 10m by 20m, the spokesman said.
It was contained by 8pm, the spokesman said.
