A huge fire has brought some of Christchurch's busiest roads to a standstill.

Fire and Emergency were called to a building on Manchester Street about 3.30pm.

A spokesman says initially the fire was reported to be the 119 year old McLean's Mansion.

They now believe it's a nearby building.

Bealey Ave and parts of Manchester and Colombo Streets are closed.

Allana Elcock is stuck in her car and says there's a lot of smoke.

"It is probably the worst smoke I have seen since the Port Hills fire a few years ago, it's very thick smoke and quite windy as well."

Meanwhile, Christchurch Police have closed part of State Highway 1 where fire and emergency crews are battling an out of control bush fire

Main South Road is closed between Templeton and Weedons Ross roads.

Police say motorists should use State Highway 73 or go through Prebbleton.

Police have also been kept busy after they called to reports of an assault on Oxford Street this afternoon. 

A spokesperson says one person is reportedly injured, and another has been taken into custody.

They say the Armed Response Team attended as a precaution, as there were concerns the person was armed.