A woman has died and four people have been injured in a crash near Christchurch.

The two-vehicle crash occurred on Tunnel Rd about 5.30pm and one person died at the scene, Police said.

St John said four people were moderately injured and understood the crash involved two vehicles, not one.

All were being taken to Christchurch Hospital by ambulance.

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Tunnel Rd is blocked and diversions are in place.

Canterbury Metro Commander Superintendent Lane Todd said three men and a woman were in the first vehicle when it collided with a bridge on Tunnel Road.

The woman died at the scene. The men sustained minor to moderate injuries.

"The second vehicle collided with the first before also hitting the bridge. Its driver, the sole occupant, has been taken to hospital with minor injuries."

Police are advising motorists to avoid the area if possible as Tunnel Rd is not accessible via Port Hills Rd or Ferry Rd.

Christchurch Transport Operations Centre Senior Travel Information Advisor Steven Mann said emergency services were on site and it was expected that they will be on site for some time.