All southbound lanes have now reopened, however traffic is still very heavy with long delays.
A man has been taken to hospital after a two-truck crash on the M7 at Prestons.
A NSW Ambulance spokesman confirmed a 60-year-old man had been transferred to Liverpool Hospital in a serious condition following the incident.
He is suspected to have suffered head injuries.
There are no other reports of injured persons.
Emergency services were called to the scene shortly after 2pm.
Two southbound lanes on the M7 have been closed at the exit to the M5.
Motorists travelling south on the motorway are facing significant delays.
Fire and Rescue NSW crews are working to contain a fuel spill as a result of the crash.
Drivers are still able to pass the crash site, but traffic is heavy and queued about 14 kilometres back to Horsley Park.
Motorists are advised to allow plenty of extra travel time as emergency services and traffic crews work hard to clear the crash site.
Keep up to date with the latest traffic information at livetraffic.com.