More than 200,000 people attended May Day rallies across Japan on Friday, calling for peace and nuclear disarmament ahead of a key international conference on the matter.
Monday will see the start of a confab in New York at which the Nuclear Non-Proliferation Treaty will be reviewed.
The May Day demonstrators emphasized their commitment to global peace this year, which marks the 60th anniversary of the end of World War II, organizers said.
The 76th annual events held under the auspices of the Japanese Trade Union Confederation (Rengo) drew an an estimated 201,600 people in 37 prefectures as of 3 p.m., according to a National Police Agency tally.
Rengo President Kiyoshi Sasamori told the main gathering in Tokyo's Yoyogi Park: "Peace is a basis of the labor movement. We never allow any war in order to fulfill our responsibility for global peace.
"Japan is now experiencing an increasingly bigger gap between the strong and the weak. Rengo will try to solve as many problems as possible as a representative of the weak."
Referring to Monday's deadly train accident in Amagasaki, Hyogo Prefecture, Sasamori urged corporate managers to prioritize safety over profits.
"The world-class safety dogma (of Japan's railway system) has collapsed," he said. "It is safety that they must not cut corners on."