Homes were evacuated and part of Auckland southern motorway closed after a truck carrying canisters containing highly flammable gas burst into flames.
Fire and Emergency were called to the scene just north of the Papakura on-ramp northbound just before 3am.
A police spokesperson said: "These [the canisters] have exploded over all of the northbound lanes and into the bush on the side of the road.
"The motorway was blocked and nearby properties have been evacuated as a precaution."
A woman who witnessed the fire said the flames looked nearly as tall as nearby power lines and it was a scary sight.
Police said no-one had been injured.
About 30 people evacuated from homes on Harbourside Drive were later allowed back to their houses.
Sam Durbin spent about three hours out of his home and said the experience was one he wouldn't forget in a hurry.
It was a "bit of a rough start" to the morning when the family dog came into the bedroom and woke them just before 3am.
"I woke up a bit and heard popping noises and thought, jeez, that doesn't sound like fireworks.
"So I bleary-eyed wandered to the back of the house and looked out the back and it was just absolutely orange, it was going up about fifty-odd metres to the pylons.
"There was lots of popping and projectiles being thrown into the air along with massive amounts of smoke."
Outside, neighbours were gathering on the road and Fire and Emergency crews were telling people to evacuate, Durbin said.
The burnt-out truck. Photo: RNZ / Felix Walton
Truck operator Chemcouriers - a Mainfreight company - said it did not yet know why the vehicle caught fire.
The fire has been put out, and all lanes of the southern motorway reopened before 10am.
Auckland's southern motorway was closed between Papakura and Takanini to both northbound lanes due to the truck fire, and did not fully reopen until mid-morning. Photo: Waka Kotahi NZTA Auckland
Though diversions were put in place the closure left traffic at a virtual standstill.
Air New Zealand had to delay up to 10 flights by around 45 minutes each because staff were stuck in traffic, the airline said.
One motorist told RNZ he had been been stuck in traffic for at least four hours from 4am.
Twelve fire trucks were at the scene at the peak of the blaze.
"Massive amounts of smoke" - Sam Durbin