UPDATE: Two dead after car carrying seven people rolls on freeway northwest of Melbourne

A second man has died in hospital after a car crash northwest of Melbourne overnight.

Investigators believe a vehicle carrying seven people rolled several times after the driver lost control on the Calder Freeway in Madecon.

Police are now looking at what caused the car to roll.

A 20-year-old man died at the scene, while five others sustained injuries.

There are traffic diversions currently in place around the scene of the accident on the freeway.