The driver of a silver SUV is being sought after a man sitting in a vehicle was fatally shot in the head in Victoria.

He was killed about 8.20am on Tuesday in Labilliere Street in Bacchus Marsh.

Police are still trying to formally identify the victim, but believe he's a 48-year-old Bacchus Marsh man.

Detective Senior Sergeant Steven McIntyre has appealed for the driver of a silver SUV seen by witnesses to come forward.

It's believed the vehicle fled the scene and was last seen heading south on McCrae Street.

The victim was shot dead while sitting inside this Ford van. (9NEWS)

There are reports of an argument in the street about an hour before the shooting, however police are unsure if there is any connection between the two incidents.

Police won't say how many shots were fired or what type of gun was used.

"At this point in time it seems to be an isolated and confined incident," Snr Sgt McIntyre said.

Police at the scene in Bacchus Marsh. (9NEWS)