Metro has expressed its regret after a 72-year-old grandmother, who had no more than 10 seconds to load her two small grandchildren and bags onto a train, was left stranded on the platform while the children were carried away without her.

On November 3, Clare Hassard, 72, was at Southern Cross Station, attempting to board a Frankston-bound train with her granddaughters, aged four and five, when the doors closed while she bent down to pick up her luggage.

A Metro investigation of the incident using CCTV footage found less than 11 seconds elapsed between the last passenger exiting the door Ms Hassard and her grandchildren were entering and the driver closing the train doors. The train doors were open for 18 seconds in total, and it took 13 seconds for the doorway to clear and for Ms Hassard to help the children on board. She then walked to the yellow safety line to collect her bag, but within five seconds the doors had closed, and three seconds later the train departed.

Another adult on the train accompanied the children to Flinders Street Station, where the family was reunited with the assistance of Metro staff.

Metro took until Friday, 26 days, to respond to a complaint by Ms Hassard's son Anthony Ryan, who is also the children's father.