The atomic-bombed city of Nagasaki has set up a countdown board to mark the number of days until next year's UN treaty to ban nuclear weapons goes into effect.

The Treaty on the Prohibition of Nuclear Weapons reached the necessary 50 ratifications on Saturday.

Japanese swimming star Ikee Rikako delivered a speech at an event marking the start of the one-year countdown to the Tokyo Olympics.

The Tokyo organizing committee held the closed-door event on Thursday at the National Stadium, the main venue for the games.