Hiroshima Mayor Kazumi Matsui urged world leaders to do more to realize a world without nuclear weapons in a peace declaration he read out in English on Monday.
'I truly appreciate Bangladeshi people who show sympathy to the victims and express strong message for peace, ' he said in a message marking the Hiroshima Day that falls on August 6.
More than 300,000 people across China were killed by Japan's biological weapons during WWII.
The skies over Hiroshima's Peace Memorial Park were clear, just as they were on Aug 6, 1945, when an American B-29 bomber dropped its deadly payload on the port city dotted with military installations, ultimately killing 140,000 people.
"Our nation, while maintaining our (non-nuclear weapons) principles, will patiently work to serve as a bridge between the two sides and lead efforts by the global community" to reduce nuclear weapons, Abe said.
Participants in Monday's ceremony - survivors, Prime Minister Shinzo Abe and representatives from 80 countries - observed a minute's silence at 8:15 a.m., the moment when the USA dropped its payload on the unsuspecting population 73 years ago.
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The anniversary comes amid hopes to denuclearise North Korea after Kim Jong Un and President Donald Trump made vague aspirational statements of denuclearising the peninsula when they met in Singapore in June.
Prime Minister Shinzo Abe, attending the memorial ceremony, pledged that Japan will try to bridge nuclear powers and non-nuclear states and lead worldwide efforts. Matsui urged leaders to steadily work toward achieving a world without atomic weapons, and called on Abe to help the Treaty on the Prohibition of Nuclear Weapons take effect.
Over two years, the group of Japanese high school students has been painstakingly producing a five-minute virtual reality experience that recreates the sights and sounds of Hiroshima before, during and after the US dropped an atomic bomb on the city 73 years ago.
"Maintaining its three nonnuclear principles, our country is determined to make strenuous efforts to serve as a bridge between both parties", Abe said.
In Ashland Monday morning, a brief ceremony marked with the sound of a gong signaled the beginning of a four-day ceremony and the moment when the first of two atomic bombs exploded onto the world stage.
Atomic bomb survivors and many visitors prayed for peace at the Peace Memorial Park near Ground Zero under the scorching summer heat. Their average age is at 82.06, highlighting the challenge facing Japan of passing down their experiences to future generations.