And one of them got a hug. Shigeaki Mori, 79, appeared overwhelmed with emotion as he shook hands with US President Barack Obama after a highly-charged ceremony in Hiroshima.

"The president gestured as if he was going to give me a hug, so we hugged," Mori said of the embrace that was broadcast around the world.

That very human moment between an old man and one of the world's most powerful people came after Obama delivered a soaring speech that touched on the horrors of the American atomic bomb that obliterated Hiroshima.

"71 years ago, death fell from the sky and the world was changed," Obama told a specially-invited audience at the Hiroshima Peace Memorial Park.

"Why did we come to this place, to Hiroshima? We come to ponder a terrible force unleashed in the not-so-distant past. We come to mourn the dead," he said.

Mori was a young boy when he was blown into a river by the force of the huge blast on August 6, 1945.

He saw dead and dying people everywhere, many with their innards hanging out, and says he was only able to escape the horror by clambering over the barely-breathing bodies all around him.

Obama also met the sprightly Sunao Tsuboi, a 91-year-old who suffered serious burns in the blast and subsequently developed cancer.

Tsuboi, a long-time campaigner for nuclear disarmament, smiled broadly as he shook Obama's hand, with the two men for upwards of a minute.

"I was able to convey my thoughts," a satisfied Tsuboi told reporters afterwards.

Tsuboi suffered burns all over his body during the attack, and wandered naked through the charred streets until he could no longer walk, before collapsing in the radioactive dirt.

"I told him to firmly study what exactly nuclear weapons are," he said, adding that he appreciated Obama's visit.

"I give him a big welcome. His Prague speech is still alive."

Tsuboi was referring to a landmark address Obama gave in the Czech capital in 2009 when he called for a "world without nuclear weapons," a sentiment he reiterated yesterday in Hiroshima.

For Mori, the emotion of the meeting with Obama was all a bit much. Asked what exactly the two men had talked about before he got his hug, he confessed he didn't quite know.

"I tried to listen to him, but it was so overwhelming," he said.

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