The sole city to fall victim to an atomic bomb attack holds its annual peace memorial ceremony with the mayor of Hiroshima calling for a world free of nuclear weapons by 2020.
Tens of thousands of people from all over the globe observed a moment of silence on Thursday at Peace Memorial Park in the Japanese city to honor the 140,000 victims of the blast 64 years ago.
Hiroshima Mayor Tadatoshi Akiba urged world leaders to unite in the quest for the abolition of the remaining nuclear warheads by the end of the year 2020 -- a call echoed by Japanese Prime Minister Taro Aso, who also spoke at the ceremony.
"The abolition of nuclear weapons is the will not only of the hibakusha but also of the vast majority of people and nations on this planet," Akiba said as he delivered a peace declaration.
"Japan will continue to uphold its three non-nuclear principles and lead the international community toward the abolishment of nuclear weapons and lasting peace," Aso adhered.
Solemn 'hibakusha' (atom bomb survivors) were among the 50,000 people who gathered near the A-bomb Dome, the skeleton of a hall charred after the United States, under the then president Harry S Truman, dropped the nuclear bomb Little Boy on the city at 8:15 am on August 6, 1945.
The fallout from its mushroom cloud killed some 140,000 people, instantly or in the days and weeks that followed, due to radiation or horrendous burns.
Three days after the attack, the US dropped a second atomic bomb named Fat Man on the southern port city of Nagasaki, killing more than 70,000 people.
The old foes have been close allies following Japan's August 15 surrender that ended World War II in the Pacific. Japan now hosts some 47,000 US troops.
Washington has never apologized for the decision to nuke Japan, which 64 years onwards still sparks hot debate over the necessity of the move.
Some say the blasts were a sacrifice of thousands for the good of millions.
However, many, including senior officials of the time, have questioned the motivations behind the bombings that some deem experimental atrocity.
"It always appeared to us, atomic bomb or no atomic bomb, the Japanese were already on the verge of collapse," Henry H. ("Hap") Arnold, the then commanding general of the Army Air Forces, declared in his 1949 memoirs.