The historic Waipa Tavern in Ngāruawāhia has gone up in flames overnight.
The fire service received multiple calls around 2am to the blaze at the north Waikato pub, which was more than 100 years old.
Assistant commander Blair Kiely said the fire had been fully contained to the tavern and had only been fought from the outside.
"To the best of our knowledge the building was derelict," he said. "No crews have been able to enter the building due to the safety hazards associated with the structure."
Firefighters were on Sunday morning dampening down hotspots. Specialist fire investigators were at the scene.