At least six people have died and others remain unaccounted for following a fire in a hostel, New Zealand's prime minister has told local media.

Emergency services were called to the four-storey Loafers Lodge hostel in Wellington just after midnight local time.

More than 50 people were rescued from the building, but police said 11 people remained unaccounted for.

PM Chris Hipkins warned the number of dead was likely to increase.

Police added that they could not be more specific on the number of deaths until they could access the building.