Peak hour chaos after crash backs traffic up 10km

Traffic was backed up at least 10 kilometres after a shocking eight-car crash on a Melbourne freeway this morning.

Authorities were called to the Princes Freeway in Laverton after the smash just after 6.30am today.

The crash forced the closure of two lanes, with traffic quickly backing up at least 10 kilometres.

Six people were treated by paramedics but did not require hospital treatment.

Lanes have since reopened but there are significant delays in the area.

It's not clear what caused the crash during the morning rush. 

Thousands of commuters were left sitting bumper-to-bumper as they waited to pass the crash.