Dunedin City Council chief building control officer Neil McLeod said two parapets on the three-storey Rattray St building started falling about 8.50am, causing the roof to cave in.
The top two levels were vacant but the ground floor housed the Dragon Cafe.
"It doesn't appear to have damaged the restaurant at all," Mr McLeod told NZPA.
"The operators of the cafe would have been at home in their beds because they work 'til late each night.
"They will get a bit of a surprise."
Despite there being no damage, the cafe would not be able to reopen for at least a couple of days - until dangerous parts of the parapets were removed. It was possible it would remain closed for several weeks until an engineering assessment had been conducted.
"They will then throw some tarpaulins over the hole in the roof to make it weatherproof and then the engineers will make a further assessment," Mr McLeod said.
"I would expect the work to be completed within two or three days and the engineering assessment probably a couple or three weeks after that."
The area around the building was closed while the damage was assessed today, and the power and gas were disconnected.
The nearby Crown Hotel was evacuated as a precaution, and the road remained closed.
Mr McLeod said there was "nothing exotic" about the incident.
"We had another parapet fall over before Christmas that really caused no stir in the city at all simply because it didn't involved closing a major street," he said.
That, too, was a commercial building.
Asked whether strengthening work was needed on the city's older buildings, Mr McLeod said: "I think you could argue that some of the older buildings could do with some maintenance."
Building owner Lincoln Darling referred inquiries to his insurer. However, he said he had owned the building for five years and had not received any requests to strengthen it.
