Women on the Japanese island chain of Okinawa on Wednesday demanded an apology from an outspoken Japanese politician who suggested US troops there make use of its thriving sex industry.

The comments from Osaka Mayor Toru Hashimoto followed earlier comments that "comfort women" - who most historians agree were pressed into sexual slavery for the Japanese imperial army during World War II - served a "necessary" role in keeping soldiers in line.

Twenty-five women's groups in Okinawa issued a statement claiming to be a voice from Okinawa, which still sits in the midst of unhealed scars of war and daily violence imposed by the military.

"We strongly protest against the Hashimoto comment and demand an apology and retraction of the remark," the statement said.

The Chinese government also expressed shock and anger over the comments. Hong Lei, spokesman with the foreign ministry, said the comments publicly challenged history and betrayed basic ethics.

Hong said that coercing women into being "comfort women" was a serious crime, adding that how Japan treats the past will decide its future, and its neighboring countries and the international community were waiting for Japan to make its choice.

Shoko Toguchi, a senior member of a women's rights group, said Hashimoto "lacked the sense of human rights and was not able to feel the pain of Okinawa's people," Jiji Press reported.