Wellington: At least six people died as a fire broke out at a hostel in the New Zealand city of Wellington, media reports said on Monday.

The incident left 20 people injured.

It's believed the original blaze broke out at the Loafers' Lodge in Newtown soon after midnight local time (10pm AEST), reports 9 News.

"It is a truly tragic situation, the worst outcome," Wellington Mayor Tory Whanau said.

Police have not commented on the fire publicly.

"There's a risk of the roof caving in and, of course, we need to make sure that our firefighters are protected as well," Whanau said.

According to Stuff, a number of people still remain unaccounted for.

There were about 94 people in the hostel at the time of the fire, the property manager told Stuff.