Updated 6.37pm: The flames have died but some Cantabrians are yet to return home after a blaze ripped across semi-rural properties in south-west Christchurch.

Firefighters have spent the day struggling to contain up to 60 fires across the region.

Two homes were burned in a blaze that spread across a swathe of properties in Yaldhurst.

Acting Fire Regional Commander Dave Stackhouse says conditions have eased and the number of firefighters in the area has now been scaled back.

He says there will be a managed process to help people return to their homes.

About 30 to 40 homes were evacuated as a precautionary measure at the height of the fire.

Dave Stackhouse says anyone concerned about returning to the scene of the fire should visit the welfare centre at Hornby Primary School.

The two homes burnt in the blaze have minor to severe damage.

The cordon on Roberts Road is still in place between Matangi Street and west to the 100km speed sign on Roberts Road.

All other roads have reopened and residents are returning to their properties.

Cameraman Joe Morgan, who was at the scene, said he saw the fire cross a paddock in “10 to 15 seconds flat” before smoke filled the area and explosions were heard from a nearby house.

“It ripped across an open paddock ... it skimmed over the short dry grass.”

He said some residents were saying fallen power lines, which caused a power outage shortly before the blaze began, could have been at fault. He heard an explosion and saw a fireball emerge from the burning home, he said.

“It was probably a gas tank going up in the garage.”

Bystanders said three helicopters fighting the flames had been swooping down to fill water buckets from Gilberthorpe School's swimming pool. Matangi St resident Ben Mulholland said his house was evacuated shortly after 2.30pm.

“I could smell burning and I wondered if it was anything to do with the power cut, then about 10 minutes after that I could see lots of smoke and people were driving up and down the street and yelling, ‘Get out, get out.’

“There is a lot of firemen and policemen around, a lot of fire trucks so I doubt it will get much bigger,” he said. “But in the last half hour or so they have been moving us further away, it’s probably just a safety precaution but at the same time I am assuming the worst — that perhaps it’s not 100 per cent sorted yet.”

There were hundreds of people gathered at the perimeter of the area, Mr Mulholland said.

Beckenham local Rod Cameron said a massive haze of smoke was blocking views of the Port Hills. He said smoke had drifted as far as his home — roughly 14km away. Mr Cameron said he had to close the windows in his house, as the smell of the fire filled the air.

A St John spokeswoman said no injuries had been reported.

However, Newstalk ZB's Jess McCarthy says there are reports two firefighters have collapsed and there are plenty of ambulances in the area.

"None with their emergency sirens on but they are clearly wanting to monitor these firefighters for exhaustion."