A police officer has been assaulted and a teenage girl seriously injured after a violent brawl erupted outside a train station in Melbourne's south-east.

At least 15 teenage girls and boys were involved in the melee which broke out near the Oakleigh train station on Haughton Road just before 6.30pm on Tuesday.

A teenage girl was taken to hospital in a serious condition with non-life threatening injuries, police said.

It is understood she's now in a stable condition.