Tokyo Metro has ordered its station workers to monitor station platforms more carefully after one of its workers at Roppongi Station let a train on the Hibiya Line depart Sunday without noticing that a female passenger had slipped between the platform and one of the cars.

The woman, who fell into the 25-cm gap between the platform and the stationary train, sustained no injuries. The incident took place around 9:23 p.m. in Minato Ward.

Tokyo Metro spokesman Koichi Yoshida said the woman, thought to be in her 20s, apparently saved herself by immediately evacuating to a space under the platform that measures roughly 1.1 meters high and 52 cm wide.

Her female friend yelled that someone had fallen onto the tracks to a station employee standing 4 meters away, Yoshida said, but as the worker assumed she was referring to an object rather than a person, he told her that he would pick it up after the train departed.

The employee, 20, who only joined the company in April, did not check before allowing the train to leave.

Once the train pulled out of the station, the woman's friend climbed down to the tracks and helped her back up to the platform. The two told the employee that they were fine and caught the next train without identifying themselves, Yoshida said. No trains were delayed.

The train's driver was unaware of the incident because it took place while the train was stationary. The conductor in the last car also didn't realize what had happened because the place where the woman fell was a blind spot due to the curved platform.