One of the first people on the scene of today's gas explosion in Christchurch has spoken of the horror that they encountered.

The explosion destroyed one house on Marble Court, in the suburb of Northwood, and damaged several others. Six people have been injured and rushed to hospital - with injuries ranging from moderately serious to critical.

Bradley Culver was having a cup of coffee and watching the Open Championship golf on TV when the explosion happened.

The former police officer ran outside and saw a neighbour's house completely destroyed.

Several people were trapped in the debris of timber and mortar.

Culver and others started to drag them free.

They were stunned, in total shock, he said.

The survivors were pulled free with cuts, scratches and bruises but no major injuries, Culver said.

They were all aged in their 50s and 60s.

"I am surprised nobody died [instantly]," Culver said.

"As a former police officer I've seen a lot in my days but I've never seen anything like that."

Culver says he's shaken by the event.

The house where the explosion happened is totally destroyed, he said.

Chunks of roof tiles scatter the surrounding streets.

Another nearby resident, Indraj Fonsaka, revealed he was nearly blown off the toilet.

"It nearly knocked me off. I thought it was an explosion underground," said Fonsaka, who lives across the street from the blast.

His wife Akita was screaming from the garage.

They ran to each other and couldn't believe what they saw.

Pink Batts were raining from the sky and the house across the street was destroyed.
They both thought it was a meteor strike.

Styx Mill Country Club employee Tom White said concrete tiles from the roof of the 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, its blown the garage door right off the next-door neighbour's house."

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

"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."

Newstalk ZB Christchurch host Chris Lynch said earlier that callers from across the city say they heard an explosion with some residents in Redwood saying their houses shook violently.

City councillor Aaron Keown is on the scene and he says the windows of the neighbour's house have completely blown out. He says a pre-school is 100 metres away and is going to check on children.

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 down from the sky on to her property.

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

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 says the debris is 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."