A motorcyclist carrying a stubby has collided with an unmarked police car south-east of Melbourne.

The unregistered motorcycle struck the rear passenger side of the police vehicle on Frankston-Flinders Road in Baxter about 1.45am on Sunday.

police Credit:Erin Jonasson

Police said the motorcyclist, a 45-year-old Baxter man, tried to ride away after the incident.

"The rider, carrying a stubby, tried to flee the scene before he collapsed off the bike a short distance away," Leading Senior Constable Julie-Anne Newman said.