The 18-year-old man, of Pakenham, was struck near Officer station around 1.45am on Sunday, only days after two people were killed on the tracks in Altona Meadows.

Police have been told the teenager was walking between the tracks about 500 metres east of the station when he was hit by an eastbound train, a police spokeswoman said.

He suffered critical head injuries in the incident, an Ambulance Victoria spokesman said.

He was taken to The Alfred hospital in an air ambulance, where he remains in a critical condition.