The Loafers Lodge caught alight overnight, prompting an evacuation at the four-storey hostel in the southern Wellington suburb of Newtown.

Around 90 emergency personnel responded to the blaze, which was doused around sunrise on Tuesday.

Aerial trucks winched around five people to safety from the roof of the hostel, which was reportedly at capacity.

Officials were privately bracing for dozens of fatalities earlier on Tuesday but inspector Dean Silvester said police’s initial assessment was that “fewer than 10” had died.

“We are not in a position to be any more specific until we can access the building,” he said.

A small number of people are also being treated at Wellington Regional Hospital, which is 100 metres away.

News outlet Stuff reports the fire is being treated as suspicious by police.

Emergency services are now working to secure the hostel so they can gain entry and assess for damage and loss of life.

Fire and Emergency New Zealand (FENZ) district manager Nick Pyatt said “it doesn’t get worse than this” for his crews.

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

“This is a tragic event for all involved. My heartfelt condolences go to the loved ones of those who have lost their lives.”

Emergency crews hope to be inside the building within hours.

Prime Minister Chris Hipkins, who left parliament on Tuesday morning to visit the site, said it was “quite confronting”.

“We’ve not seen an event of this scale for quite some time,” he said.

“Wellingtonians will feel this. Wellington is a small community. It’s a tight knit community.

“I want to, on behalf of the whole country, extend our support to the first responders who are on the scene, particularly our firefighters, our police, our ambulance services and others.”

There were no vacancies at the hostel, which is also used for transient housing, except for a number of rooms being treated for bedbugs, Radio NZ reported.

Mayor Tory Whanau, who described it as a “truly tragic situation”, said the building housed a mix of short and long term residents, including emergency housing tenants.

“Possibly a lot of vulnerable folks which makes this even more devastating,” she told AAP.

“We’ll find out more in the coming hours and days.

“Wellington is feeling deep sadness and sorrow at what has happened.”

Fire and Emergency NZ deputy national commander Brendan Nally said they were working through a list of occupants.

“In the chaos this morning people fled the scene which is completely understandable,” he said.

“Given the nature of the occupants of this building it has been somewhat difficult to track everyone down … that’s why I’m urging everyone to be cautious with numbers.

“Among those we know have been deceased, we are also aware of quite a few that we can’t say this is where they are and they are okay.”

Police have urged anyone with information around the whereabouts of occupants to come forward.

The devastating fire recalls the burning of the Palace Backpackers Hostel in Childers, Queensland, 23 years ago, which killed 15 people.

Most of the dead were overseas travellers who’d come to harvest local crops.

It was later discovered itinerant fruit picker Robert Paul Long had set the century-old timber building on fire after being kicked out the week before.