One person is missing after a massive blaze engulfed the under-construction Sky City Convention Centre in central Auckland.

Workers had been evacuated as black smoke could be seen climbing into the Auckland skyline and people were told to stay out of the CBD.

Firefighters were struggling to contain the blaze and gale-force winds were forecast to cause more problems later in the day.

Workers claimed the fire started when a blow torch left unattended ignited flammable material on the roof of the building.

About 100 firefighters are tackling the fire in the seven-level building.