WELLINGTON - A fire at a hostel in New Zealand killed at least six people on Tuesday and officials said they believe the toll could rise with 11 people still missing.

The blaze broke out on the top floor of Loafers Lodge in the Wellington neighbourhood of Newtown just after midnight, police said. The cause of the fire is not known.

"This is a once-in-a-decade fire for Wellington. It’s the worst nightmare for us," District Manager Commander Nick Pyatt said in a statement.

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

Loafers Lodge resident Tala Sili said he saw smoke coming under his door and opened it to find the hallway full of smoke. He decided to jump out the window onto a roof two floors below.

"It was just scary, it was really scary, but I knew I had to jump out the window or just burn inside the building," he told state-owned Radio New Zealand.

Firefighters are on the scene as there are still small fires inside the building, and structural and risks assessments are being undertaken. Investigations into what caused the fire are under way, according to Fire and Emergency New Zealand (FENZ).

Police said they will not have more information until the 92-room building is safe to enter, and there remains a risk the roof will collapse.

Prime Minister Chris Hipkins told breakfast television show AM that six were dead and police said that they expect the death toll will be fewer than 10.

Hipkins visited the site and spoke with emergency service providers.

"It is an absolute tragedy and it is a horrific situation," Hipkins told media after the visit.

"In the fullness of time, of course there will be a number of investigations about what has happened and why it happened but for now, the focus needs to be on dealing with the situation."