An unsettling wake up call for residents of a group of flats in the Christchurch CBD.

One tenant woke to a fire in the roof just before 1.30 this morning, and called emergency services.

Fire Service spokesperson Andrew Norris says crews went into the ceiling to put the fire out at the flats in Armagh Street.

The fire service was able to keep the blaze contained, thanks to the prompt alert.

A dozen fire fighters attended and one appliance remain at the scene although the fire's out.

Mr Norris said they're still unsure if alarms were installed and how many people were inside, but no one was injured.

The cause of the blaze is yet to be determined.