Firefighters have extinguished a fire on the third floor of a multi-story apartment block in Willis St, Wellington, this afternoon.

Fire and Emergency Assistant Commander Matt Franklin said multiple 111 calls were received and the apartment was fully involved in fire when the first crews arrived shortly after 2.30pm.

"We responded swiftly and in numbers, extinguished the fire and conducted a full search of the building. Fortunately, no-one was home in the apartment," he said.

There is smoke on all levels and firefighters have been ventilating the building.

Six fire trucks, one aerial appliance (ladder truck), a command unit and operational support vehicles attended.

Specialist fire investigators have begun work to establish the origin and cause of the fire.

As at 4pm there were still road closures in place and people are asked to avoid the area so as not to delay the movement of emergency services.

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