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 fire has been put out but northbound lanes of the southern motorway remained closed and were not expected to open for some time.

"There is a significant amount of debris to clean up off the road and the fire is still burning out.

"There are diversions in place but as commuters will understand, this is going to cause significant delays and we would strongly advise people to avoid travelling this morning if they don't need to."

Twelve fire trucks were at the scene at the peak of the blaze.