HIROSHIMA, Japan (AFP) - - The Japanese city of Hiroshima on Wednesday marked the 63rd anniversary of the world's first nuclear attack amid hope the next US president will work for the abolition of atomic weapons.

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" 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, which was also addressed by local school children.

"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," said 11-year-old Honoka Imai.

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 bomb survivors and activists gathered in Nagasaki this week to protest against the arrival of a US nuclear-powered submarine, just days after it emerged another vessel may have leaked a small amount of radiation earlier this year.