Police are on the hunt for a man who committed a lewd act on a bus in Glen Waverley directed towards a 17-year-old girl.

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Police were told a man got on a bus at Glen Waverley Railway Station and engaged in sexual activity directed at the girl at around 11.05am on Friday, 21 April.

He is described as medium build with a bald head and short grey hair on the sides and may also be using a crutch or walking stick.

The man was last seen wearing a black coat and blue jeans with a grey shopping trolley and a green bag.

Anyone who recognises the man or has information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report at www.crimestoppersvic.com.au

Image: Victoria Police