Two trucks and a car have crashed on the Western Ring Road, causing major traffic delays on multiple freeways as a semi-trailer lies stranded on its side in the middle of the road.

The smash happened at about 10.25am, Victoria Police said in a statement. Three Greensborough-bound lanes near Pascoe Vale Road on the Ring Road are still closed, with only the left lane open.

VicRoads said it did not know when the road would fully reopen. Police estimate the road may be closed for six to eight hours while the truck is unloaded and moved, affecting the peak hour drive home.

Drivers are being advised to exit the Western Ring Road as early as possible and detour via Camp Road before re-entering from Sydney Road.

The truck, which contains detergent, is lying across four lanes. Traffic is at a standstill behind the crash site for several kilometres. The smash has already created major traffic jams in the northwest, causing delays on the Tullamarine and Calder freeways, according to the Age.

"VicRoads is working closely with emergency services to get the lanes open as quickly as possible," it said in a statement. "We are monitoring traffic on the detour routes and adjusting traffic lights to assist with congestion, where possible.

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"The truck is loaded with boxes of soap and needs to be unloaded by hand, due to the weight of the load. The truck is too heavy to move while loaded."

A truck driver was injured in the crash and taken to hospital for observation.