There was traffic chaos on the freeway on Friday following the incident, which happened at 4.50am.

Hours later, a second crash on the same freeway led to another round of extensive delays.

VicRoads reported heavy traffic following the second collision - a six-car pile-up - which happened just before 10am near the English Street overpass.

In the earlier, pre-dawn incident, the minibus - with a driver and five passengers - had tried to turn around but was hit from behind by a truck while attempting the U-turn, a police spokeswoman said.

The minibus then rolled on its side, blocking traffic on the busy freeway.

Paramedics treated six people at the scene, three for minor injuries, but no one needed to be taken to hospital, an Ambulance Victoria spokesman said.

The driver of the truck was not injured.

The right lane was closed near Mickleham Road after the smash and it took hours before the resulting traffic delays were cleared.

Victoria Police would not reveal whether the mini-bus driver could be fined or face charges over the U-turn attempt.

Officers are continuing with the investigation, police said.

No one was injured in the second incident, which closed one lane of the freeway.