Southbound traffic on the M7 was closed at Eastern Creek following a six-vehicle crash on Friday afternoon.
Emergency services were called to the scene after four heavy vehicles and two cars collided about 1.30pm.
Two people have been injured in the incident.
The occupants of a Mitsubishi Pajero, a man and a woman, were trapped inside their car in the wake of the crash.
They were released and taken to Westmead Hospital with non-life threatening injuries.
Motorists were advised the avoid the area after the crash.
Reports say traffic was backed up as far as 15 kilomteres from the site of the incident.
Lanes were reopened about 4.30pm. Buses travelling around Eastern Creek were experiencing delays of up to 35 minutes.
“Traffic is still very heavy in both directions, so motorists should continue to allow plenty of extra travel time and expect significant delays,” a Transport Management Centre spokesman said.
“Motorists travelling south are also advised to exercise caution as work continues in the closed lane to clean up soil spilt from one of the trucks.
“Emergency services and motorway crews remain at the scene.”
An investigation is underway.
Anyone with information should contact Crime Stoppers, 1800 333 000.