Sixty seven years ago an atomic bomb was dropped on the city by the United States by the orders of then President Harry Truman.
The bomb contained the equivalent of between 12 and 15,000 tons of TNT and devastated an area of five square miles and more than 60 per cent of the buildings in the city were destroyed.
More than 140,000 people were killed out of the city's population of 350,000 including military personell and those who later died from radiation.
Many have also suffered long-term sickness and disability. Another atomic blast in Nagasaki three days later killed 70,000 more.
The grandson of ex U.S President Harry Truman has also chosen to take part in the memorial services and attended a service for victims.
Clifton Truman Daniel visited the Hiroshima Peace Memorial Park on Saturday and laid a wreath to show his respect.
'I think this cenotaph says it all - to honor the dead to not forget and to make sure that we never let this happen again,' Daniel said after offering a silent prayer.
Daniel, 55, is in Japan to attend ceremonies next week in Hiroshima and Nagasaki and his visit is the first by a member of the Truman family.
Daniel, a former journalist said in a statement that he decided to visit Hiroshima and Nagasaki because he needed to know the consequences of his grandfather's decision as part of his own efforts to help achieve a nuclear-free world.
He said he hoped to hear stories from survivors about how they overcame their adversity. Daniel will also meet with the mayors of Hiroshima and Nagasaki and participate in discussions with students.
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