Firefighters believe a blaze at a Christchurch car workshop spread from a pile of waste and general rubbish, but it's not clear how it started.
An alert has been issued because of the smoke coming from the fire, which is billowing across the city.
Incident controller Dave Key said the fire was contained but still burning.
Fifty firefighters and 10 fire engines were battling the Sydenham blaze.
Key said they know where the fire began but were still investigating what caused it.
He said roads around the workshop would be closed for much of the day but crews aimed to get at least part of Colombo St reopened by about 10am.
Crews would be at the scene all day and using heavy machinery to turn over the site.
That meant the smoke would be coming and going throughout the day, Key said.
Other businesses ran out of the same building that the workshop was in and would be affected, he said.
Emergency services were called to Auto Inspection Services on Colombo St shortly before 4.30am on Thursday, a Fire and Emergency New Zealand spokesperson said.
The large fire was still burning, the spokesperson said and parts of Colombo and Durham Sts, around the building were closed and would remain so for some time.
A police car and ambulance were also at the site, an RNZ reporter said.
The smoke drift was affecting the Sydenham, Addington and Spreydon area, Fenz said.
It issued an emergency alert warning people to stay indoors if possible, keep doors and windows closed and be mindful about using air condititioning units.
"If you have any health concerns please call Healthline or 111 in an emergency".
At this stage it was too early to say what had caused the fire, the spokesperson said.
It was believed it would take some time to extinguish the fire due to the size of the building.
No injuries have been reported.
