Police and Metro have warned of a growing "subculture" of criminal and dangerous behaviour on Melbourne's rail network, after a young man was critically injured while train surfing on Wednesday night.

Metro figures show train surfing happens about once every six weeks on average in Melbourne, the City Loop tunnels are invaded 10 to 12 times a year and "coupler riding" - where people ride on the back or outside or a train - happens more than 100 times a year.

Metro chief executive Andrew Lezala said train surfing and coupler riding were problems all over the world, but in his view Melbourne had a bigger problem than other cities.

"You get this kind of behaviour on most train networks but it seems to be a lot worse here than I've seen elsewhere," Mr Lezala said.

The 23-year-old man from Albert Park suffered life-threatening head injuries and was rushed to The Alfred hospital after train surfing from Bentleigh station to McKinnon station in Melbourne's south-east.