The cause of a fatal early morning inferno in a Christchurch boarding house remains unclear, but suspicious circumstances have been ruled out.

Photo: RNZ/Conan Young

The single storey Shaw Avenue building went up in flames just before 5.45am this morning - and it took only a matter of minutes for the sleepy New Brighton street to be packed with sirens and commotion.

When Fire Assistant Area Commander Mike Bowden fronted media later this morning, the fury of the flames was still evident, hours after being put out.

"It's a pretty good indicator if you see the toetoe bushes behind us - it's blown out, caught all those on fire," he said.

"There's a big build-up of heat in these older properties so the fire was really ferocious. I understand even the neighbours were screaming out for people to evacuate out of the building."

At the Anzac Drive Fire Station, two kilometres away, the calls for help started at 5.47am, he said.

Swift acting firefighters got the blaze under control less than 15 minutes later by containing the flames to the front bedroom.

Silvio Bezerra woke in his sleepout at the back of the property and managed to alert one of those living in the house to the flames, before they both ran out to the street.

"The flames were powerful, not too much smoke but ... super, super hot," he said.

For the man sleeping in the front bedroom, the fire proved fatal.

Victim will be 'sorely missed'

The police haven't named the victim but his friend, Karen Holmes, said he was a talented artist who would be sorely missed.

"He loved travelling and he had a love for nature. He was searching [for a place to live] - he'd been in a flat here then gone away and done some travelling then come back here to settle."

She said she was in shock at the loss of her friend, who came over for a cup of tea yesterday and to watch the movie Horse Whisperer with her.

But amid the shock and grief, Mike Bowden said emergency services could have been dealing with a much worse situation, if it weren't for working smoke alarms.

"As tragic as this absolutely is, the other thing to remember is six other people were woken by the smoke alarms and have evacuated the house," he said.

Of the boarding house's six remaining tenants, just one suffered an injury in the form of a small cut to their arm.

He said Housing New Zealand's offering them short term accommodation and Work and Income's offering them financial support, while their belongings remain out of reach, behind the cordon.

An investigation into the cause of the fire is continuing.