An 18-year-old Italian student is being hailed a hero after his quick actions saved the life of a toddler who fell onto the tracks at one of Milan's busiest subway stations.

CCTV footage from Milan's Repubblica metro station shows the moment the two-and-a-half-year-old tumbled onto the tracks, just one minute before a train was due to arrive in the station.

Lorenzo Pianazza, who was on his way home after meeting with his parents nearby, jumped onto the track after the boy, also finding time to retrieve one of the child's toys.

Mr Pianazza followed the child onto the tracks with moments to spare. ( ABC News )

Mr Pianazza told local media he was never fearful for his own safety, he just acted on instinct and adrenaline when he saw the toddler in imminent danger.

"I saw that at the arrival of a train there was a minute-and-a-half, I knew I could do it [in time], and no-one else was moving. They were stuck, [the bystanders] stopped and looked on," Mr Pianazza said.

"I'm happy to have done what I thought was right to do and not caused more trouble stepping down on the tracks."

Meanwhile, the station manager on shift, Claudia Flora Castellano, saw the whole thing unfold on the monitors from the control room.

She told the Milan Courier she followed procedure and pressed the red button to stop the train as soon as she saw what happened.

Lorenzo Pianazza and Claudia Castellano are being hailed as heroes for their actions. ( Facebook: Beppe Sala )

The readiness of Ms Castellano and the fast actions of Mr Pianazza were praised by Milan's Mayor Giuseppe Sala, who invited the duo to his office following the incident.

"Today we have witnessed a brave gesture. Thanks to your readiness and that of the station agent which stopped the movement of trains a child was saved," Mr Sala said on Thursday.

"I would like to … thank you both on behalf of the whole city of Milan."

The pair also met with the parents of the child who was seemingly unharmed in the terrifying incident.

"[Mr Sala] called me, he wanted to meet us all, including the mother of the child," Mr Pianazza said.

"The mother of the child has already thanked me, the important thing is that the child is back in her arms, the rest does not matter.

"I do not even want to imagine what it must feel like to be in [the mother's] situation."

He said despite the outpouring of thanks and support from the public, he did not feel like hero.

"They're saying I was brave … I was just ready," he said.