Four people have been injured following a serious crash in the Selwyn District this afternoon.

A St John spokeswoman said that all four patients were on route to Christchurch Hospital - two in a critical condition with the other two patients were moderate.

Three ambulances and other emergency services attended the scene, with a helicopter also dispatched.

Police said the crash occurred on Waimakariri Gorge Rd between Darfield and Springfield around 4.15pm.

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Diversions are in place at Curve and Pinegrove Rds off SH73 - the road is not suitable for heavy vehicles.

Police are asking motorists to consider Old West Coast Rd as an alternative route.

The Serious Crash Unit has been advised of the crash.