Nagasaki's mayor called on nuclear weapons-possessing nations and their allies to "show courage" by breaking free from nuclear deterrence principles on Wednesday at a scaled-down ceremony to mark the 78th anniversary of the atomic bomb attack on the city.

Due to a tropical storm, the ceremony at the Nagasaki Dejima Messe conference center became the first since 1963 to take place inside rather than at the city's Peace Park close to the hypocenter where the bomb detonated.

Authorities in the city have decided to hold this year's event among organizers only and cancel in-person attendance, including by Prime Minister Fumio Kishida and international guests. It was the first Nagasaki ceremony not to be attended by a Japanese leader since 1999.