At least six people have been killed in a fire that broke out in a hostel in New Zealand's capital Wellington, Prime Minister Chris Hipkins said on Tuesday.

"It is an absolute tragedy," Hipkins said.

New Zealand's head of government said that there were likely to be more than six fatalities. Police have said they expect the death toll will be less than 10.

So far, 11 people have been registered missing. 

"We have yet to fully reconcile a list of all of those people who were here last night, we will not speculate on how many people were here and where they have gone," said Acting District Commander for Wellington Police Dion Bennett.

The cause of the fire is still unclear, police said. 

Firefighters said 52 people had been rescued, some from the roof of the building.

What we know about the fire

The fire broke out on the top floor of the Loafers Lodge hostel in the Wellington suburb of Newtown. 

The hostel provided residence for construction workers, hospital staff and those serving sentences in the community for minor crimes. 

Emergency services were called to the hostel shortly after midnight local time. 80 Firefighters and 20 trucks battled the blaze through the night.

Nick Pratt, an official for Fire and Emergency Services New Zealand (FENZ), said that such fires are rare.

"This is a once-in-a-decade fire for Wellington," he said. "It's the worst nightmare for us."

Crews remained on the scene of the fire as of Tuesday morning. An FENZ statement said that there was still a risk of roof collapse.

Rescue workers said there are still small fires inside the building and structural and risk assessments are underway.

One of the main roads into Wellington has been closed and traffic is being rerouted.

Australian Prime Minister Anthony Albanese told the media that he spoke to Hipkins and offered assistance. "This is a dreadful human tragedy," he said.

sdi/fb (AFP, AP, Reuters)