A Christchurch pub has been damaged in an early morning blaze.

Fire and Emergency southern shift communications manager Tim Reynolds said the alarm was raised about 3am at a commercial building in Main North Rd, Papanui.

The roof of the building was engulfed by fire but there were no reports of injuries, he said.

At the height of the blaze seven fire crews were needed to quell the flames.

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Reynolds said one fire crew remained at the scene.

Fire safety investigators were expected to arrive at first light to work out what sparked the blaze.