A broken expansion joint on a major road into Melbourne is being blamed for traffic bedlam on the western fringe of the city this morning.

Drivers heading towards the city on the Princes Freeway at Werribee are still experiencing delays this morning due to a road surface issue that led to a truck overturning and a subsequent car crash.

Reports indicate that a metal plate, which was covering the expansion joint, became dislodged overnight. Around 4:20 am, a truck hit it while traveling at 100 km/h, causing the vehicle to tip over onto its side.

That crash then triggered a pile-up of up to 10 cars, causing the closure of multiple lanes of traffic near Duncans Road.

While one lane towards Melbourne has been reopened, two lanes remain closed as teams continue to examine the situation and work on safely reopening all lanes.

No one has been injured.

Earlier in the day, delays exceeded two hours on the freeway and on surrounding roads through Werribee and Wyndham Vale.

Those delays have eased slightly, with motorists now facing about an hour of extra time on the road.

Motorists travelling between Geelong and Melbourne can save time by detouring via Bacchus Marsh and the Western Freeway.

Travellers can also avoid delays by taking V/Line trains on the Geelong line.

Drivers are being urged to be patient and mindful of local traffic, and obey all local speed limits if travelling through Werribee.

Authorities say all lanes will reopen when investigations and repairs are complete and it is safe to do so.