State Highway 1 is now open in both directions following a serious crash involving a caravan near Wellsford.
Motorists are advised to continue to expect delays as traffic congestion eases.
The incident happened shortly after 1pm between Wellsford and Warkworth, near Wayby Valley Rd.
A woman was seriously injured and is being airlifted to hospital, police said.
Three other people have been taken by ambulance to North Shore Hospital, one in a moderate condition and two with minor injuries.
