The woman was suffering a medical condition and fell onto platform two at the station in the City Loop just before 4pm.

The only other person waiting on the platform immediately informed Metro staff members, who made sure all trains approaching the station were stopped.

Commuters helped the injured woman onto the the platform and an ambulance arrived to take her to hospital.

Cranbourne, Pakenham and Frankston line trains were diverted to Flinders St Station during the emergency.

A Metro Trains spokeswoman said all lines were back running to schedule for peak hour.