Christchurch explosion: House's gas supply had just been fixed

Emergency services are being praised for their response to a freak gas explosion in a Christchurch suburb.

Friday's blast in Northwood turned one house to rubble and damaged surrounding properties.

Northwood Residents Association President Clive Smith says the police and other first responders have been amazing.

"Police have basically worked at securing the properties, and in the follow-up setting up an emergency centre in the Styx Mill Country Club. It's been great."

Five people remain in hospital with a range of injuries.

Smith says the community has come together.

"We've had a number of people who have opened up their homes and said they're available for these people, sometimes for as long as they like. It's been overwhelming."

Emergency services are still trying to figure out what caused the explosion. Stuff reports a gas contractor was working in the house on Thursday, making repairs.

About 50 residents were evacuated from surrounding properties as a precaution. A dozen homes were expected to remain empty overnight.

"Safety experts have been going from house to house within the outer cordoned area to ensure these homes are safe for people to return to," said Canterbury Metro Commander Supt Lane Todd.

"We appreciate this has been a difficult day for the approximately 50 residents who had to leave under such traumatic circumstances."

"What we're really concerned about initially is making sure they've got the basics... and these first two days, as far as accommodation is concerned," said Smith.

Five nearby properties were affected by fire, and  17  impacted by debris.

WorkSafe is investigating the blast, as are police and Fire and Emergency NZ. 

The blast was so big, it was picked up as magnitude 2 shake.

Newshub.