A witness earlier said they believed at least a dozen cars were destroyed in the blaze in carpark 14, at the bottom of the hospital campus, about 50m from any hospital buildings.
The man, who did not want to give his name, works at the hospital’s Child Health Centre which overlooks the carpark.
“We started hearing a few small explosions,” he said.
“There was lots of black smoke and probably, in total, at least a dozen vehicles destroyed.”
He had noticed the flames in a couple of cars just after 2pm on Tuesday and called Fire and Emergency New Zealand on 111.
A witness believes at least a dozen cars have been destroyed in the blaze.
While his call wasn’t the first to 111, the fire spread from car to car before firefighters arrived.
The flames had been fanned by the steady wind, he said.
The man thought the fire probably started in just one car but spread along the row where the cars were packed in.
“It’s a very busy carpark, it’s normally full during the day.”
A nearby resident out walking down by the Raumanga Stream was stopped by police, who pulled out a rope, telling her she couldn’t go any further as it may be a crime scene.
Police have asked people to avoid the area while emergency services respond and for residents living nearby to close their windows.
Resident Harmony Muller was on her way home with her daughter when she noticed thick, black smoke.
She said she “was thinking, oh my gosh, I thought it was my house”.