The Crash Investigation Unit are working on the scene of a crash on the M1 at Cooranbong which involved 4 cars.

NSW Ambulance have confirmed a male in his 70s was airlifted to John Hunter Hospital in a serious condition with head and chest injuries.

Another male in his 50s was transported to the John Hunter Hospital in a stable condition with minor injuries.

The M1 Motorway remains closed in both directions between Palmers Road and Mandalong Road with diversions in place.

Police say a crime scene has been established and will be examined to determine the circumstances surrounding the incident.

It is expected there will be traffic diversions in place for some time while specialist police conduct the examination.

Police are asking for anyone who witnessed the incident or has dashcam footage to contact them.