Police and FENZ warned residents to keep their doors and windows closed. Crowds gathered to watch as the blaze sent smoke billowing across South Auckland.
In an emergency alert sent to residents, FENZ said: "Residents south east and up to 1km down wind of Parker St, Papakura are advised to put in house protection in place including closing windows and doors due to large smoke hazard from burning cars and buildings in the area."
Police said there are cordons in place at Calvert St and Hunua Rd, Boundary Rd and Hunua Rd and Boundary Rd train tracks (near Otuwairoa Stream).
Roads are expected to be closed for some time, and motorists and pedestrians are asked to avoid the area.
Papakura resident Dave Fern said he could hear bangs and explosions.
"A few minutes ago, there was a really big one and the house actually shook. We were in the lounge and the fireplace chimney started rattling. The whole house shook just like a short, sharp earthquake.
"We were out shopping and [as we were] coming home we saw the thick smoke in the sky. There were very thick billows of smoke and it spread a long way, being carried by the wind. We heard lots of sires and bangs," Fern said, who lives about one km from the site."
Police officers are on the scene helping Fire and Emergency NZ with traffic management.
