Visiting Auckland couple John and Jenny Hayes and their party of six were in Monty's admiring the fire when they heard "a roar, someone thought it was a helicopter over the top", Mrs Hayes said.
Mr Hayes said, "We started seeing smoke coming back down the chimney and thought, that doesn't look right, and had a look outside to see what happened."
Grey smoke billowed from the upstairs of Monty's. Patrons, staff and onlookers gathered on the street, while firefighters wearing breathing apparatus entered the premises.
The fire was put out at 6pm.