Police believe a grey Kia had pulled into the fast-food car park on The Esplanade at St Kilda in Melbourne about 10pm on Tuesday, after being followed by occupants in stolen white Mazda.
An unknown male exited the Mazda and started banging on the Kia, before its 17-year-old passenger was slashed with a weapon near the drive-thru entry.
Detectives said the Mazda followed the Kia as it left the car park and travelled toward Acland Street, then down St Leonards Avenue, where it hit a dead end.
The occupants inside the Kia attempted to flee the scene on foot, with the teenager found with serious injuries nearby and taken to hospital.
"Police believe the teen was deliberately struck by the Kia," a spokesperson said.
The group in the Mazda dumped the vehicle, before they stole the Kia, police said.
The vehicle was found nearby and officers have been told two male occupants of African appearance fled from the vehicle towards Beaconsfield Parade.
Detective Inspector Mark Patrick told reporters at the scene the crimes were very serious.
"The offenders have no humanity, these offenders — behaviour like dogs, rabid dogs is what I'd call these behaviours," he said
No arrests have been made, and large-scale search continues.
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