A witness, Alex, was walking down the street when he spotted flames.
"I was Pokemon-hunting when I actually saw the flames...[and] saw the smoke. I turned the corner and that's when I noticed that [the flames] were all kind of bursting up through skylight windows, so it must have obviously been building up quite big inside.
"It was bursting out the sky-lights and then starting to catch fire on the bigger building next-door to it.''
Lichfield and Tuam streets have been closed between Colombo and Manchester streets, Transport for Christchurch says.
A spokeswoman for St John confirmed they received a call to assist about 5.15pm.
The blaze has now been categorised as a third alarm.
A spokeswoman for the southern fire communications said they were dealing with "an event'' and could not take any calls at the moment as a result.
Authorities are telling motorists to avoid the central city.
"Motorists are recommended to use Moorhouse Ave as an [alternative] to Tuam St and Lichfield St."