A quick-thinking bystander has rescued a young boy from the path of a train in a terrifying incident in Melbourne's south-east.

Horrified commuters spotted the young boy wandering along railway tracks near Narre Warren station about 12.45pm on Tuesday.

A young boy has been rescued from the path of a train. Credit:Eddie Jim

Witness Louise Barnes, of Footscray, said a woman in her 20s sprinted onto the city-bound tracks to grab the boy, who was aged about three.