1247 GMT February 23, 2020
The visit came hours after a highly symbolic stop in the city of Nagasaki, where Pope Francis assailed against all nuclear weapons, including their use as a deterrent, AFP wrote.
At least 140,000 people were killed after the United States dropped the first atomic bomb on Hiroshima on August 6, 1945, with a second nuke that killed another 74,000 people in Japan when the American military dropped its second nuclear weapon on Nagasaki three days later.
About 400,000 others lost their lives in subsequent months, years and decades of radiation sickness or illnesses.
"In barely an instant, everything was devoured by a black hole of destruction and death. From that abyss of silence, we continue even today to hear the cries of those who are no longer," Francis said at the Peace Memorial in Hiroshima.
"With deep conviction, I wish once more to declare that the use of atomic energy for purposes of war is today, more than ever, a crime not only against the dignity of human beings, but against any possible future for our common home," he added.
Pope Francis has made the call for a world without nuclear weapons a central theme of his four-day trip to Japan, starting his visit in two cities synonymous with the horrors of the atomic bomb.
He said he felt a "duty to come here as a pilgrim of peace" and paid tribute to the "strength and dignity" of those who survived the attack and the physical and emotional toll of the aftermath.
Like in Nagasaki earlier on Sunday, he laid a wreath of white flowers as a tribute and bowed his head in prayer before a moment of reflection with deep bells tolling in the background to remember those killed in the catastrophe.
True peace is 'unarmed'
Survivors from Hiroshima described to the pope their personal experiences and backed his abolitionist message, including Yoshiko Kajimoto, who was 14 at the time of the attack.
She recalled "people walking side by side like ghosts," telling Francis: "No one in this world can imagine such a scene of hell."
The ageing survivors of the attacks have expressed fear that the memory of the bombings may disappear after their death, and some hope the pope will bring renewed attention to their stories.
In Hiroshima, the Argentine pontiff repeated his insistence that there was no place in the world for nuclear weapons, even as a deterrent.
This marks a break with past pontiffs – in a 1982 UN speech, Pope John Paul II described nuclear deterrence as a necessary evil.
"How can we propose peace if we constantly invoke the threat of nuclear war as a legitimate recourse for the resolution of conflicts?" Francis said.
"A true peace can only be an unarmed peace."
In Nagasaki earlier, he also took aim at the arms industry, describing money spent and made on weapons as an "affront crying out to Heaven".