Some 45,000 people, including Prime Minister Yasuo Fukuda, gathered at a memorial to the dead within sight of the A-bomb dome, a former exhibition hall burned to a skeleton by the bomb's incinerating heat on August 6, 1945. They stood and offered silent prayers at 8.15 am local time on Wednesday, the exact moment in 1945 when a single US bomb instantly killed more than 140,000 people and fatally injured tens of thousands of others with radiation or horrific burns.
Speaking on the occasion, Hiroshima Mayor Tadatoshi Akiba said the United States was one of only three countries that were still opposed to a UN resolution submitted by Japan calling for the abolition of nuclear arms.
With the average age of survivors now over 75, Akiba was quoted by the Sydney Morning Herald as saying that authorities in Hiroshima would launch a two-year scientific study of the psychological impact of that experience.
The annual ceremony was made more meaningful with the presence of a Chinese representative. Each year, the city invites representatives of the world's eight declared nuclear powers to the event. Previously India, Pakistan and Russia were the only nuclear powers that had sent representatives to the ceremony. The other declared nuclear states - Britain, France, North Korea and the United States - have never come.
Three days after the Hiroshima bombing, the United States dropped a second nuclear bomb on Nagasaki, which killed another 70,000 people in the southern port city.
Japan surrendered in World War II on August 15. The nation has since been officially pacifist and turned into one of the closest US allies.