Victoria Police spokeswoman Natalie Webster said: “Police are currently at the scene of an incident in Bacchus Marsh where a man has died.
“Emergency services were called to Labilliere Street just before 8.20am after it’s believed a man in a vehicle sustained a gunshot to the head.
“Detectives from the Homicide Squad are en route to the scene.
“The exact circumstances are yet to be determined however at this time the death is being treated as suspicious.”
Ambulance Victoria confirmed paramedics didn’t transport the man to hospital.
Schools in Bacchus Marsh were locked down as a manhunt begun for people seen fleeing the scene.
Bacchus Marsh Grammar school, which is about 1km from the scene of the fatal shooting, sent text messages to parents alerting them to a police “incident”.
“Upon notification of an incident the school went into lockdown at 9.45am,” the message read.
“After discussions with police the lockdown was lifted at 10am.
“All students and staff are safe and well.”
Nearby primary schools were also locked down.
Detective Senior Sergeant Stephen McIntyre said an argument had been heard by witnesses prior to shots being fired.
“We have a deceased male in the driver’s seat of a white van,” he said.
“Witnesses have seen a silver SUV type vehicle pull up near the intersection of Labilliere St and McCrae St at the driver’s side of that vehicle and shoot the man sitting in the driver’s seat.
“We have commenced investigations at this stage as to who this offender is.
“We would make an appeal at this point in time for the driver of that silver SUV to make himself known to the police.
“At this point in time we are not saying it is a silver Ford Territory until we can confirm that.”
Snr Sgt McIntyre said police had not yet identified the victim and the silver SUV was last seen speeding away south along McCrae St.
“There were witnesses in the vicinity at the time,” he said.
“We have had reports of an argument occurring in the hour or so prior to the incident.
“We are keeping an open mind as to whether that is connected to the shooting.
“We are keeping an open mind as to whether the gunman was alone or left with someone.”
Police refused to say how many shots had been fired or what type of gun was used.
“It seems to be an isolated and confined incident,” Snr Sgt McIntyre said.
“The relationship between who has shot the victim and the victim himself is yet to be established.