In the first incident two young people were stopped by a dark-coloured station wagon with red and blue flashing lights in Wantirna South on Monday night. When they were threatened by a man with a gun, they reversed their car into a power pole but managed to flee from the scene.
A short time later, the occupants of the station wagon threatened the driver of another car at Ferntree Gully.
The offenders stole the driver’s keys but were unable to start the vehicle, which was fitted with an immobiliser.
In the third incident, a man was ordered to get out of his car at South Yarraa and the offender then drove off in it.
Three men, from Craigieburn, Moonee Ponds and Deer Park were arrested on Tuesday and have been remanded in custody. They were charged with a number of offences including armed robbery, impersonating police and firearms charges.