The Second World War holds different meaning for each generation, because of the different memories they have formed about it, said Prime Minister Lee Hsien Loong in Tokyo on Thursday, before illustrating the point with his personal stories of what he remembered.

"My generation didn't live through (the war) but we know from our parents what it was like - and their stories. If my father had been taken away, he would not have come back and I would not be here today. My uncle - my mother's brother - was taken away, and never came back. So these memories mean something," he said.

He also said he remembered clearly when sites of mass graves of people killed during the Japanese Occupation were uncovered in Singapore in 1962, because one of the sites was beside his school, and he saw people digging up the graves.

But Mr Lee noted those from his children's generation would be further removed and have fewer memories of the war, just as those from his parents' generation would have much more painful memories, having lived through it.

Mr Lee was speaking at the Nikkei Conference on the Future of Asia, and made the comments as he was answering a question about the rise of nationalist sentiment in Japan and the desire among some Japanese to change its pacifist constitution.

It was the prerogative of any country to decide how to write its constitutions, but it is also the responsibility of the government to "make the wisest choice" on it, he said - before pointing out how WWII memories lingered to different extents among various countries and generations.