This is the moment a heroic passenger crawled under a train to save a toddler who accidentally fell into the gap between the train and the platform.

The little boy and his parents were about to board the G1228 train at Nanjing South Railway Station in China when he accidentally slipped on Monday afternoon, November 4.

He fell into the gap between the train and the platform and became stuck. Other passengers and station staff rushed to help pull him out, but they could not reach him as the boy was too far down.

A passenger named Liu Fengyuan stepped in to help. In the footage, he is seen tapping the train conductor to move out of the way before squeezing into the gap and crawling under the train.

Within seconds, Liu managed to grab the boy and pull the child and himself to safety.

Liu's colleague, Zhang Yawei, caught the rescue on video and told local media that they were on a business trip when the incident happened.

Liu also spoke to reporters and explained that, as a father of two children, he understood how any parent in that situation would feel deeply concerned.

He said: "I didn't think about anything else; I just took off my coat and said, 'Let me go down.'"

Liu added: 'It was just a small effort. I really didn't think too much about it at the time.'

Nanjing Railway Station later confirmed that the boy was unharmed and that he and his parents continued their journey.