Four patients are being taken to hospital - two in critical condition - after a multi-car collision near Makarewa this afternoon.

Emergency services have been attending the serious road traffic accident on State Highway 6 (Winton-Lorneville Highway) since just before 4pm.

Two helicopters and three ambulances have been sent to the scene, according to a St John spokesperson.

Two patients were critical, one patient was seriously injured and one had a minor injury, he said.

Three patients were being taken to Southland Hospital and one was being taken to Dunedin Hospital.

A Southern police media spokeswoman said at least two cars had collided just before 3.58pm on State Highway 6 near North Makarewa-Grove Bush Road and Counsell Road.

Diversions are in place and the road will remain closed overnight. Motorists were being asked to avoid the area or expect delays.