The Hume Motorway is closed northbound at Woodlands due to a car crash just past Greenhills Road.
Motorists in light vehicles are being diverted onto the Old Hume Highway to travel via Berrima.
This diversion is not suitable for heavy vehicles, which are being parked.
Traffic is very heavy, so motorists are advised to allow extra travel time and expect delays.
Motorists already in the area should also follow the directions of emergency services and traffic crews on site.
A medical helicopter is on the road.