Survivors, relatives and a handful of foreign dignitaries attended this year's main event in Hiroshima to pray for those killed or wounded in the bombing and call for world peace. But the general public was kept away, with the ceremony instead broadcast online.
Participants, many of them dressed in black and wearing face masks, offered a silent prayer at exactly 8:15 am (2315 GMT Wednesday), the time the first nuclear weapon used in wartime was dropped over the city.
Speaking afterwards, Hiroshima mayor Kazumi Matsui warned against the nationalism that led to World War II and urged the world to come together to face global threats, like the coronavirus pandemic.
Japan's Prime Minister Shinzo Abe, who has been criticised by some for his attempts to revise a key pacifist clause of the country's constitution, pledged in his address to "do my best for the realisation of a world without nuclear weapons and peace for all time".
At 8:15 a.m. on Aug 6, 1945, US B-29 warplane Enola Gay dropped a bomb nicknamed "Little Boy" and obliterated the city with an estimated population of 350,000, where thousands more died later from injuries and radiation-related illnesses.
On Thursday, as cicadas shrilled in the heavy summer heat and the Peace Bell sounded, the crowd stood to observe a moment of silence at the exact time the bomb exploded.
The Atomic Bomb Dome, or Genbaku Dome, was the only structure left standing in this district of the city and has been preserved as a peace memorial.