A serious crash involving a car and a motorbike has closed the southbound lanes of State Highway 73 (SH73) at the Lunns Road intersection in Middleton, this morning.

Emergency services were called to the scene at 5.40am on Friday.

Road (SH73) is currently blocked at the Lunns Road intersection.

St John responded with one ambulance and three rapid response units.

One patient was transported to Christchurch Hospital in critical condition.

The rider of the motorcycle is the patient being treated for life-threatening injuries.

The Serious Crash Unit is investigating the incident, and police have said the intersection will likely remain closed for several hours.

While the road remains open to northbound traffic, access from the northbound lanes into Lunns Road is currently unavailable.

Motorists are advised to expect delays, use alternative routes, and allow extra time for travel as emergency services continue to respond.