Watch: 'It's matchsticks' - gas blast destroys Christchurch house, six hurt

The victims of a house explosion may have survived because they were close to the source of the blast, a fire chief says.

Six people were injured in the suspected gas explosion in Northwood, Christchurch this afternoon. One person was in a critical condition, three were stable, one has been transferred to Middlemore Hospital and the other patient has been discharged.

Fire and Emergency area commander Dave Stackhouse said they were relatively lucky to be close to the centre of the explosion.

"Often with these types of things it's the blast wave that can actually kill people further away from the actual radius of the initial explosion.

"So I guess we are lucky that we are not looking at multiple fatalities here."

It appeared six properties had been significantly damaged - one completely - by the explosion.

Stackhouse said all of Northwood was connected to piped gas, but at this stage it was not clear how there had been a leak.

"We've got our gas experts having a look at that," he said

"Once we've got the scene safe ... we'll look at what's caused this and carry out an investigation with police and WorkSafe."

Canterbury Metro Commander Superintendent Lane Todd said this evening that cordons and security would remain overnight around 12 homes that were in the immediate area around the explosion. Police were ensuring the residents had a place to stay.

Other residents who were evacuated after the blast were being allowed to return home this evening.

Todd said safety experts were going from house to house within the wider area to make sure the homes were safe to return to.

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

This morning's explosion sent debris flying 100 metres in all directions and left the house looking like "matchsticks".

One of the first neighbours on the scene, former police officer Bradley Culver said he was amazed no one was killed.

Belinda Blanchfield told Stuff four members of her family and a family friend were inside the home at the time.

The explosion was "our worst nightmare", she said.

Blanchfield's husband Paddy told Stuff there had been problems with gas earlier this week and the family were waiting for repair work to be carried out. He was not sure if that work had happened.

In all, 50 residents were evacuated and taken to the Styxx Mill country club immediately after the explosion.

The blast destroyed one house and caused significant damage to those surrounding it. Residents in the area were evacuated after the gas explosion. Photo / Amber Allot

Country Club employee Tom White said concrete tiles from the roof of the exploded house had been blown 100m in every direction.

"The house is matchsticks. It's totally blown apart."

"It's caused a lot of destruction to other houses, it's blown the garage door right off the next-door neighbour's house."

The blast sent debris flying 100 metres in all directions and destroyed a Christchurch home. Photo / James Looyer

I don't often post here but anyone else in christchurch here a loud, sonic boom kind of noise a few moments ago? the building here shook!!

— jasper force (@JasperForce) July 18, 2019

A neighbour who lives one block over said the explosion shook his house and knocked items off his windowsill.

The blast blew out the glass on windows in a neighbour's house. Photo / Amber Allott

"We're okay but there are houses closer which are stuffed," he said.

"The house where the explosion was - you wouldn't even recognise it as a house now.

"I think there are definitely some injuries. They got them out [of the house] but it could be serious."

Maria Lee heard the boom in Burwood, about 15 minutes away from Northwood.

"It was like a sonic boom, a massive boom," she said.

"Our dog just about crapped himself."

Newstalk ZB Christchurch host Chris Lynch says callers from across the city say they heard an explosion. Some residents in Redwood said their houses shook violently.

The gas explosion completely destroyed a Christchurch house and injured five people. Photo / James Looyer

A worker at a nearby motel and holiday park said the explosion shook nearby homes and sounded like a bomb had gone off.

"It was more than an earthquake, you'd think a bomb had gone off."

She said insulation and small debris had fallen from the sky onto her property.

"We've had housing insulation raining down on our property so something's obviously had quite a large explosion."

Five people are believed to be injured in the explosion. Photo / James Looyer

She said she suspected a gas explosion had occurred.

The explosion shook all the houses around and the woman said nearby residents had been coming over to the motel to check if everyone was alright.

"For the staff and everyone, it was certainly scary."

A bystander said the debris was spread across the road.

Graham Henderson, who works at Owls Nest Preschool about two blocks away from the explosion, said staff initially thought it was an earthquake.

"We heard the sound but because we're carers we've got to keep calm.

"It wasn't dissimilar to a quake. And that's what we are used to around here.

"It wasn't until a parent called that we found out it was an explosion."

"The kids are fine," he added. "We've had a few worried calls from parents but they have just keep playing."

Facebook users reported hearing what sounded like an explosion from various parts of the city - Avondale, Bryndwr, Woolston, Parkland and Redwood.

- additional reporting: Christchurch Star