Japan has marked the 70th anniversary of the atomic bombing of Hiroshima in a ceremony in the city.

Prime minister Shinzo Abe and foreign delegates were among those observing a moment of silence at the Peace Memorial Park in downtown Hiroshima at 8:15am (local time), when the detonation turned the western Japanese city into an inferno.

Bombing Hiroshima "Little Boy" was the nickname of the 10,000-pound uranium 235 bomb

"Little Boy" was the nickname of the 10,000-pound uranium 235 bomb American B-29 Superfortress bomber Enola Gay dropped the bomb

American B-29 Superfortress bomber Enola Gay dropped the bomb It exploded 600m above Hiroshima, setting off surge heat reaching 4,000 degrees Celsius across a 4.5km radius

It exploded 600m above Hiroshima, setting off surge heat reaching 4,000 degrees Celsius across a 4.5km radius By the end of 1945, casualties reached 140,000 out of an estimated population of 350,000

By the end of 1945, casualties reached 140,000 out of an estimated population of 350,000 Japan has recognised the total number of victims who died of radiation injuries in Hiroshima as 253,008

Japan has recognised the total number of victims who died of radiation injuries in Hiroshima as 253,008 The city of Kokura was the secondary target had Hiroshima been overcast Source: Reuters

The now-bustling city's mayor, Kazumi Matsui, said nuclear weapons were an "absolute evil" as he urged the world to put an end to them forever.

"To coexist we must abolish the absolute evil and ultimate inhumanity that are nuclear weapons. Now is the time to start taking action," he said in his annual speech.

One elderly man attending the ceremony told the ABC he saw the mushroom cloud from the bomb go up on August 6, 1945.

"My grandmother, school mates and relatives were all killed by the bomb," he said.

"The wind blew in our direction and then I heard a loud bang — the sound came later as it was about two kilometres away.

"We were thrown onto the ground."

Another elderly survivor paying her respects said: "I have become sick so I felt I had to come here this year. I've asked those who are already on the other side to come for me soon."

An American B-29 bomber named Enola Gay dropped an atomic bomb, dubbed "Little Boy", on Hiroshima on August 6, 1945, in one of the final chapters of World War II.

Nearly everything around it was incinerated, with the ground level hit by a wall of heat up to 4,000 degrees Celsius — hot enough to melt steel.

This year another 5,000 victims' names were added to the cenotaph, bringing the total number of deaths caused by the bombing to almost 300,000.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 6 minutes 22 seconds 6 m Eleanor Hall speaks to North Asia correspondent Matthew Carney about the anniversary on The World Today. Download 11.7 MB

On August 9, the port city of Nagasaki was also attacked with an atomic bomb, killing more than 70,000 people.

Japan surrendered days later, on August 15, 1945, bringing the war to a close.

Doves fly over the Peace Memorial Park at a ceremony in Hiroshima. ( Reuters: Toru Hanai )

Opinion remains divided about necessity of attacks

Bells tolled and Mr Abe laid a wreath at the ceremony attended by US ambassador to Japan Caroline Kennedy and other officials.

Mr Abe said Japan would redouble its efforts to bring about a world free of nuclear weapons.

"And that resolve translates us to propose a new draft resolution at the United Nations this autumn on nuclear disarmament," he said.

Under-secretary for arms control Rose Gottemoeller attended the ceremony, the most-senior US official sent from Washington to the annual memorial.

Opinion remains divided over whether the twin attacks were justified.

Under the famous Hiroshima dome, one of the few buildings left standing after the bombing, protesters staged a "die in", demanding an end to atomic weapons.

But the biggest protests were against the Japanese government's push to re-interpret Japan's pacifist constitution and let troops fight overseas again.

"Mr Abe forced the Security Bill through. The method of proposing the bill was too forceful and against democracy and I don't understand it," one protester said.

While some historians say they prevented many more casualties in a planned land invasion, critics have said the attacks were not necessary to end the war, arguing Japan was already heading for imminent defeat.

Dropping the bombs, which were developed under strict secrecy, was hugely popular with war-weary Americans at the time, and 70 years on a majority today still think it was the right thing to do.

Fifty-six per cent of Americans surveyed by the Pew Research Centre in February said using the atomic bomb on Japanese cities was justified, compared to 79 per cent of Japanese respondents who said it was not.

Paul Tibbets, who piloted the Enola Gay, said he never had any second thoughts about dropping the bomb, telling a newspaper in an interview in 2002, five years before his death: "I knew we did the right thing".

Washington, which has been a close ally of Tokyo since the war, has never officially apologised for the bombings.

Japan's prime minister Shinzo Abe (right) and other dignitaries mark the anniversary of the atomic bomb attack on Hiroshima. ( Reuters: Thomas Peter )

Timeline of Atomic Bombings September 1, 1939: World War II begins

September 1, 1939: World War II begins December 7, 1941: Japan bombs Pearl Harbor, US enters WWII

December 7, 1941: Japan bombs Pearl Harbor, US enters WWII August 13, 1942: The Manhattan Project officially starts

August 13, 1942: The Manhattan Project officially starts July 16, 1945: The Trinity Test (first nuclear bomb test) is done

July 16, 1945: The Trinity Test (first nuclear bomb test) is done August 6, 1945: Bombing of Hiroshima

August 6, 1945: Bombing of Hiroshima August 9, 1945: Bombing of Nagasaki

August 9, 1945: Bombing of Nagasaki August 12, 1945: United States contacts Japan to accept surrender

August 12, 1945: United States contacts Japan to accept surrender August 15, 1945: Japan announces surrender on radio

August 15, 1945: Japan announces surrender on radio September 2, 1945: World War II officially ends Source: NPR

ABC/Reuters