A teenage boy has sustained serious head injuries falling from a Sydney train, with major delays across a number of train lines as a result.
The boy, aged in his mid-teens, is understood to have fallen from the train at St Peters.
Paramedics were called to Bedwin Rd at St Peters about 5.45am.
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The boy, aged in his mid-teens, was taken to the Royal Prince Albert Hospital in a serious condition.
NSW Police were also called to the scene.
7NEWS understands the boy suffered serious lacerations to the head, and was with friends who travelled to the next stop to get help.
It took some time to remove the boy from the tracks, which had a significant impact on the train network as some services were stopped.
The T3 Bankstown Line, T4 Eastern Suburbs and Illawarra Line and South Coast Line have been affected.
Trains may now stop at different platforms and may be delayed, and stops may change at short notice.
Commuters have been urged to allow extra travel time.