It’s understood services were disrupted when the train came to a stop once he was spotted.
Sydney trains CEO Matt Longland said the trains weighed 400 tonnes and travelled up to 110km/h.
“All too often we see lives taken by people trespassing in the live rail corridor, risking their lives,” Longland said.
“It only takes a train accelerating or braking quickly or for it to move close to infrastructure for someone to be knocked onto the tracks.”
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He said 11 people had died from “illegal trespassing” in the last five years.
“Sydney Trains is working closely with NSW Police to deter ‘buffer-riding’, utilising the thousands of CCTV cameras along rail corridors to identify criminals.”
Penalties for trespassing can be up to $5500.
Customers who spot illegal behaviour are urged to use help points and notify the guard.