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.
They stood up and offered silent prayers at 8:15 am, 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.
Delivering a speech at the memorial, Hiroshima mayor Tadatoshi Akiba noted the United States was one of only three countries which oppose a UN resolution submitted by Japan calling for the abolition of nuclear arms.
"We can only hope that the president of the United States elected this November will listen conscientiously to the majority, for whom the top priority is human survival," he said.
Akiba said the effects of the atomic bombing on the minds of survivors had been underestimated for decades, adding that "the voices, faces and forms that vanished in the hell" had never left the hearts of survivors.
With the average age of survivors now over 75, he said the city would launch a two-year scientific study of the psychological impact of the experience.
"This study should teach us the grave import of the truth, born of tragedy and suffering, that the only role for nuclear weapons is to be abolished," the mayor told the service.
On the eve of the anniversary, children gathered in front of the Atomic Bomb Dome for a lantern march. Survivors burned incense before dawn broke.
An altar at the Peace Memorial Park quickly filled up with a mountain of flowers. A group of South Koreans performed a traditional dance to honour the dead, who included a number of Koreans.
"Children who evacuated buildings or went to work at factories on that day have not returned 63 years on... the atomic bomb deprived them of normal life," 11-year-old school girl Honoka Imai told the service.
A Chinese representative, a diplomat, attended the annual ceremony for the first time in a move welcomed by the city, which each year 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, hosting more than 40,000 US troops.
Dozens of atomic survivors and activists protested in Nagasaki this week as a US nuclear-powered submarine arrived in Japan, just days after it emerged another sub may have suffered a small radiation leak earlier this year.
Copyright © 2008 AFP