UPDATE: Trains to remain at crash site in Melbourne's west for probe

Two trains that collided in Melbourne's west are expected to remain at the crash site until tomorrow while investigators figure out what went wrong.

The rear-end collision between an eastbound Metro train and a V/Line train about 7pm last night left nine people, including seven passengers, suffering minor injuries.

Police said the passenger train with about 60 people on board came to a stop near a level crossing in Altona when the train from Geelong, carrying only a driver and conductor, ran into its rear.

A spokeswoman from Public Transport Victoria said the Office of the National Rail Safety Regulator was now investigating.

"Until the investigation is finished they will be staying where they are," she said.

Metro says they can route trains around the crash, meaning services are not impacted.

However, V/Line is running trains to Werribee and buses the rest of the way to Melbourne.