There's been a serious crash south of Christchurch.

Emergency services were called to the accident between a car and a truck just after 10am near Rolleston.

Three ambulances are on the scene.

St John say there is one patient with moderate injuries.

State Highway one is blocked between Dunns Crossing Road and Burnham Road.

Diversions are being put in place and motorists are being asked to avoid the area.

Police are not releasing any more details at this stage.