Hiroshima marked the 67th anniversary of the world's first atomic bomb attack on Monday with a call for the elimination of nuclear arsenals.

About 50,000 people gathered in the Japanese city's peace park near the epicentre of the 1945 blast, which destroyed most of the city and killed as many as 140,000 people. A second atomic bombing Aug. 9 that year in Nagasaki killed tens of thousands more and prompted Japan to surrender to the Allies in the Second World War.

The ceremony, attended by representatives of about 70 countries, began with the ringing of a temple bell and a moment of silence. Flowers were placed before Hiroshima's eternal flame, which is the park's centrepiece.

Relatives of victims lay wreaths at an altar in Peace Memorial Park in Hiroshima for those who died in the Aug. 6, 1945, nuclear attack on the city. (Jiji Press/AFP/Getty)

Hiroshima Mayor Kazumi Matsui said Japan must take a bolder role in leading global disarmament efforts and called on world leaders to come to his city to "contemplate peace."

He also said the nuclear accident at the Fukushima power reactor last year — an accident caused by the devastating earthquake and tsunami that struck Japan — has shown the dangers of nuclear technology, even for peaceful purposes, and urged the government to create a mix of energy sources for Japan that is safe and secure.

"I firmly believe that the demand for freedom from nuclear weapons will soon spread out from Hiroshima, encircle the globe, and lead us to genuine world peace," he said.

Matsui noted that the average survivor of the U.S.'s nuclear attack on Hiroshima is now 78 years old, and said the city is increasing its effort to provide them with health care and chronicle their experiences so the events of that day are remembered.

Prime Minister Yoshihiko Noda said Japan must pass the experience on to future generations so that the lessons of Hiroshima are not forgotten.

U.S. President Harry Truman authorized the nuclear bombing of Hiroshima in 1945, a decision his supporters say ultimately saved hundreds of thousands of civilian and soldiers' lives because it avoided the need for an invasion of Japan. Critics contend the atomic attack was unnecessary because there were signs Japan was amenable to a conditional surrender. Truman's grandson was in the Japanese city over the weekend to attend a memorial for victims.