TAIWAN President Ma Ying-jeou has urged Japan to apologise for using sex slaves from across Asia during World War II, local media reported.

Mr Ma made the call at a conference in Taiwan on sexual slavery attended by elderly women from Taiwan, South Korea and the Philippines who had been forced into prostitution by the Japanese military during the war.

"Historical mistakes can be forgiven, but the lessons of history should not be forgotten," Mr Ma said, according to the state-run Central News Agency.

"I feel that such an apology and compensation can sometimes be (most powerful)."

Time is running out as the number of surviving sex slaves - referred to euphemistically as "comfort women" by Japan during the war - is falling rapidly due to old age.

In Taiwan, a movement advocating the rights of former comfort women emerged two decades ago, when a total of 58 former sex slaves came forward, but the number is now down to eight, according to the news agency.

Historians say up to 200,000 young women, mostly from Korea but also from China, Indonesia, the Philippines and Taiwan, were forced to serve as sex slaves in Japanese army brothels.

The issue of a Japanese apology for using sex slaves is a long-running and contentious one.

In a landmark 1993 statement, then chief Japanese government spokesman Yohei Kono apologised to former comfort women and acknowledged Japan's involvement in causing their suffering.

But in remarks in 2007 that triggered a region-wide uproar, then Japanese prime minister Shinzo Abe said there was no evidence that Japan directly forced women to work as sex slaves.