The mayor of Nagasaki called Thursday for a Japan free of nuclear fears as the city marked the 67th anniversary of its World War II atomic bombing by the United States.

"Even during wartime there are certain unacceptable actions," Tomihisa Taue told a commemoration ceremony held to remember the 74,000 people who died either instantly or in the months and years after the bombing.

Taue pledged support for people whose lives have been upended by meltdowns at Fukushima Daiichi nuclear power station after it was swamped by the tsunami of March 2011.

He also called on the central government to "set new energy policy goals to build a society free from the fear of radioactivity".

The annual ceremony was held near the spot where the US military dropped its plutonium bomb, nicknamed "Fat Man", on August 9, 1945, just days ahead of Japan's surrender.

First-time attendees included Clifton Truman Daniel, 55, grandson of US president Harry Truman, who authorised the bombing of Nagasaki and of Hiroshima three days earlier with a four-tonne uranium bomb nicknamed "Little Boy", which claimed 140,000 lives.

Prime Minister Yoshihiko Noda, speaking at the ceremony, called for the abolition of nuclear weapons and pledged continued efforts to prevent the memories of the bombings from fading as survivors age.

The ceremonies to mark the anniversaries of the two atomic attacks have had greater resonance this year for many in Japan where a debate over energy policy is raging amid growing public scepticism over once-trusted nuclear power.