Six fire crews will continue to fight flare ups overnight and 100 homes remain evacuated as the scale of the Burnside fire becomes apparent.

Fire rips through logs. Photo: Chris Derrett/Derrett Photography

The Southern Motorway is closed, at least three industrial buildings have been damaged and 100 houses have been evacuated, with residents put up in hotels and motels, as a result of the fire, which started after 5pm, and continues to burn in places, despite being largely under control.

Assistant area commander and incident controller Phil Marsh said at a press conference last night six helicopters, 25 fire appliances and up to 100 staff were involved.

Three of the four fire flanks were contained, but the Kaikorai Valley end of the fire was "still creeping".

"It's not totally contained yet.'

Mr Marsh said the fire started as a vegetation fire affecting industrial premises, "spotting'' across the road into a residential area.

About 25ha of vegetation and trees were caught up in the fire, which spread to industrial buildings and a wood pile.

About 100 houses had been evacuated.

Three buildings are on fire. Photo: Olivia Franklin

Mr Marsh said a small shed was damaged at a residential property, but homes were not damaged

Three commercial buildings had been "severely damaged'', and drums of tar and oil had caught fire and exploded.

Firefighters had been withdrawn to the Concord side of the motorway, with unmanned equipment fighting the fire.

There were no reports of injuries to firefighters or residents.

The motorway was still closed last night, and the Otago Daily Times understands the main trunk railway line was also closed.

Mr Marsh said the spike in temperatures and low humidity had caused extreme fire conditions.

Three buildings are on fire. Photo: Olivia Franklin

Fire investigators would be on the scene today to determine the cause of the fire.

Dunedin City Council strategy and governance general manager Sandy Graham said about 100 homes had been evacuated.

Residents would have to stay away overnight, and motels had been organised for them, as had food and other needs.

Residents' pets would also be catered for at kennels and catteries.

Fire and Emergency New Zealand (Fenz) assistant area commander Craig Geddes said at the scene shortly before 8pm crews were "working their butts off'.

As of 9pm some crews were being stood down, but six fire crews would be stationed at strategic locations overnight to fight hot spots and flare-ups.

Helicopters would keep working as long as it remained safe, Mr Geddes said.

Mr Geddes said firefighters were "up against it'' because of spot fires, and the way the fire was travelling.

However, the fire was under control.

"We believe we have it contained to a forestry block, a wood pile and buildings adjacent to the motorway.''

Mr Geddes said helicopter crews were doing "a fantastic job'' dealing with spot fires, and controlling the main fire.

"The main issue now is the wind, which is against us.''

Helicopters battle a blaze in a large woodpile next to ABS Sandblasting on Kaikorai Valley Rd about 8pm. Photo: Mike Houlahan

There had been explosions from LPG containers, refrigerated containers and vehicles as the fire swept through the area.

"It's extremely hazardous, extremely dangerous fire conditions, with all the risks associated with that.''

At an evacuation centre at the St Clair Golf Club shortly after 8pm, about 50 people gathered from properties near the fire.

A Red Cross welfare support truck was at the scene.

People spoken to by the Otago Daily Times said they were unsure what was happening, and were waiting to hear from authorities what they should do next.

The golf club facilities were open to the evacuees, but there were no facilities for staying overnight.

A fire is burning on a hill behind the old Burnside freezing works. Photo: Peter McIntosh