Crashes have forced the closure of two major highways north and south of Christchurch, causing disruption for motorists across Canterbury.

State Highway 7 at Mouse Point Road is closed north of Leslie Hills Road, near the Hanmer Springs turnoff in North Canterbury.

Police said several vehicles and a caravan were involved, with minor injuries reported.

An NZ Transport Agency spokesperson said there were no suitable detours and urged motorists to avoid the area between Culverden and the Hanmer Springs turnoff.

Meanwhile, State Highway 1 at Chertsey in Mid Canterbury is closed following a two vehicle crash this afternoon.

Police said one person was critically injured, while another sustained minor injuries.

A detour is in place for northbound traffic via Somerton Road, Thompsons Track, Railway Terrace East and Elizabeth Avenue, before rejoining State Highway 1.

Southbound motorists should follow the route in reverse.

The detour is not suitable for heavy vehicles.