A teenage boy has been seriously injured in an incident involving a train in Sydney.

Emergency services were called to the train line between Sydenham and St Peters Stations about 8.15am on Saturday.

Police were told a 16-year-old boy had fallen from a train compartment and onto the tracks.

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Paramedics told 7NEWS.com.au the teenager suffered serious injuries to his head and limbs and has since been transported to hospital.

Transport NSW urged commuters on the T4 Eastern Suburbs and Illawarra Line to allow for extra travel time as the incident is ongoing.

“Trains may stop on platforms or between stations for longer than normal,” it said.

Services between Sydenham and Redfern have since been restored, but commuters are still urged to allow for extra travel time.

More to come...