Three arrested after Melbourne carjacking

Three men have been arrested after a carjacking on a Melbourne freeway.

A car and truck were involved in a minor collision on the Western Ring Road in Laverton North on Thursday morning, police say.

Two men from the car then flagged down a passing driver who pulled over to assist.

He was assaulted as they stole his car and sped away, hitting the truck driver, who was not injured.

The three men, one aged 25 and two aged 20, were arrested after the stolen car was found in Sunshine West later on Thursday.

The car has been towed away and will be forensically tested.