Officials have warned against a trend where young people pose on train tracks to impress social media followers.
A top Sydney transit official joined the NSW Police in condemning what he called an 'extremely dangerous and stupid' fad - one which previously made headlines in Melbourne.
Instagram pages show young people standing on train tracks and riding on the outside of city trains.
'It only takes a train accelerating quickly or braking suddenly to shake someone buffer riding onto the tracks,' Sydney Trains chief executive Howard Collins told the Daily Telegraph.
Police said riding on the back of trains or entering rail tunnels carries a $400 penalty.