A CityRail commuter says he is furious after he was trapped on a train in Sydney for almost six hours.

Mark Connelly, 34, was on his way to work when he got on an empty train at Bondi Junction in the city's east just after 9:00am yesterday.

He says the train then moved 200 metres into a recess tunnel.

"I realised what had happened and tried to get phone messages, texts or emails out to let people know I was basically trapped on the train in the tunnel but I had no reception," he said.

Mr Connelly tried finding the driver's compartment and activating emergency beacons but no one was on the train to respond.

He said he tried forcing the train doors open, breaking a window and yelling out, but finally sat down to read a book when nothing worked.

Mr Connelly waited for the next five and a half hours before a CityRail driver opened the train to get it ready for the next peak hour service.

"He was pretty surprised to see me there," he said.

Mr Connelly is urging CityRail to rethink its evacuation procedures.

"For me it was a great annoyance but I just worry about somebody who's an asthmatic, claustrophobic or diabetic or just older," he said.

"It could've been a much worse situation. There needs to be some way someone in that circumstance can communicate with the station.

"There could also be circumstances where the driver is unavailable and then there's no way for anybody in the train in emergency situations to communicate with the outside world if you're in a tunnel. And there's no way to get out. There's no emergency exit or emergency release for the doors so you're pretty much trapped."

Mr Connelly - an environment campaigner with the advocacy group Get Up - has also questioned the amount of electricity that is wasted on the trains.

"My only saving grace was that the lights and air-conditioning were still on, although I really question why the lights and air-conditioning are kept running on trains for five-and-a-half hours if they're not supposed to go anywhere and not supposed to have anyone on board," he said.

Mr Connelly said he missed out on a full day of work and an appointment to donate blood because of the incident.

Railcorp's chief operating officer, Andy Byford, has apologised to Mr Connelly and says he is investigating.

"We apologise unreservedly to the customer involved and I am trying to make contact with him to give him that personal apology," he said.

"It appears he was taken into the siding at Bondi Junction.

"We have procedures to preclude that from happening, obviously something went wrong here and we're fully investigating that.

"What we've found out to date is that the checks that should have been made appear to have been made in that there were audible announcements being made that the train was terminating, that there were visual announcements on the screens and that the staff did check the train," he said.

"Somehow we've managed to miss this customer - that's not acceptable, we will review our procedures as part of the investigation."