Survivors of the world's first atomic bombing have gathered in diminished numbers near a blasted dome to mark the 75th anniversary of the attack.

An upsurge of coronavirus cases in Japan meant a much smaller than normal turnout on Thursday - but the survivors' message for their own government and others to do more to ban nuclear weapons was more urgent than ever.

As their numbers dwindle - their average age is about 83 - many nations have bolstered or maintained their nuclear arsenals, and their own government refuses to sign a nuclear weapons ban treaty.

Amid cries of Japanese government hypocrisy, survivors, their relatives and officials marked the 8.15am blast anniversary with a minute of silence.

The US dropped the world's first atomic bomb on Hiroshima on August 6 1945, destroying the city and killing 140,000 people.

It dropped a second bomb three days later on Nagasaki, killing another 70,000.
Japan surrendered on August 15, ending the Second World War and its nearly half-century of aggression in Asia.

But the decades since have seen the weapons stockpiling of the Cold War and a nuclear standoff among nations that continues to this day.

Amid the solemn remembrances at Hiroshima's peace park, Prime Minister Shinzo Abe was confronted Thursday by six members of survivors' groups.

"Could you please respond to our request to sign the Nuclear Weapons Prohibition Treaty?" Tomoyuki Mimaki, a member of a major survivors' group, Hidankyo, implored him.

"The milestone 75th anniversary of the atomic bombing is a chance to change course."

Mr Abe insisted on Japan's policy not to sign the treaty, vaguely citing a "different approach", though he added the government shares the goal of eliminating nuclear weapons.

Even though Tokyo renounces its own possession, production or hosting of nuclear weapons, Japan is a top US ally, hosts 50,000 American troops and is protected by the US nuclear umbrella.

This complicates the push to get Tokyo to sign the treaty adopted in 2017, especially as it steps up its military role amid North Korea's continuing pursuit of a stronger nuclear programme.

Mr Abe, in his speech at the ceremony, said a nuclear-free world cannot be achieved overnight and it has to start with dialogue.

"Japan's position is to serve as a bridge between different sides and patiently promote their dialogue and actions to achieve a world without nuclear weapons," he said.

Earlier, Hiroshima mayor Kazumi Matsui urged world leaders to more seriously commit to nuclear disarmament, pointing out Japan's failures.

"I ask the Japanese government to heed the appeal of the (bombing survivors) to sign, ratify and become a party to the Treaty on the Prohibition of Nuclear Weapons," Mr Matsui said in his peace declaration.

"As the only nation to suffer a nuclear attack, Japan must persuade the global public to unite with the spirit of Hiroshima."

Thursday's peace ceremony at the Hiroshima Peace Memorial Park was scaled down because of the coronavirus pandemic.

The fewer than 1,000 attendees was one-tenth of those attending in past years.
Some survivors and their relatives prayed at the park's cenotaph before the ceremony.

"The only way to totally eliminate nuclear risk is to totally eliminate nuclear weapons," UN secretary-general Antonio Guterres said in a video message from New York for the occasion.

His expected visit to Hiroshima had to be cancelled because of the coronavirus.

"Seventy-five years is far too long not to have learned that the possession of nuclear weapons diminishes, rather than reinforces, security," he said.

"Today, a world without nuclear weapons seems to be slipping further from our grasp."

The bombing's survivors lamented the slow progress of nuclear disarmament and expressed anger over what they said was the Japanese government's reluctance to help and listen to those who suffered.

They want world leaders, especially those from nuclear-weapons states, to visit Hiroshima and see the reality of the atomic bombing.

Pope Francis sent a message to organisers of the anniversary commemoration, recalling he had prayed at the Hiroshima peace memorial during his 2019 visit to Japan and met survivors.

He repeated what he said November 24 at the peace memorial: "The use of atomic energy for purposes of war is immoral, just as the possessing of nuclear weapons is immoral."

The Holy See was among the first countries to sign and ratify the UN nuclear prohibition treaty.

Keiko Ogura, 84, who survived the atomic bombing aged eight, wants non-nuclear states to pressure Japan into signing the nuclear weapons prohibition treaty.

"Many survivors are offended by the prime minister of this country because he does not sign the nuclear weapons prohibition treaty," she said.