Emergency services were called to the Fitz Sports Bar, on the corner of Fitzgerald Ave and Cashel St, after reports of a blaze about 5am.
Four fire crews were at the scene.
The building was well involved when crews arrived, authorities say, and sent smoke across the city's business district.
NewstalkZB reporter Jess McCarthy said the blaze was under control by about 6am.
"One of the fire trucks does have its crane arm up, so potentially it was shooting water down on to the roof," she said.
"It is smoking upwards. There are not actually any signs of flames."
Officers were also in the area helping to control traffic.
The blaze, which started in the roof of the Fitz Sports Bar, forced the evacuation of a neighbouring motel - which included a group from Motueka who almost missed a national dance competition.
Angela Fox was part of a group of 10 who had travelled to Christchurch for the competition, which was scheduled to start at 8.30am.
They were woken early to a police officer banging on their door and ordering them to leave.
Fox said they only had time to grab their phones and had to stand on the street in their pyjamas.
After sheltering at another nearby motel, they were finally allowed back in to their rooms and rushed to make the competition on time.
"We all literally had half an hour to get back in to the room, get the costumes, get showered and get out. And we made it."
The cause of the fire was still being investigated.
- NZ Herald and RNZ
