A Japanese woman in her 50s has been held in Shanghai since June for her alleged involvement in spying on the country, the Mainichi Shimbun daily said.
The woman, who runs a Japanese language school in Tokyo, had visited China frequently, Kyodo News said, adding that the purpose of her visits was unknown.
Separately, another Japanese national in his 60s has been detained in Beijing on similar charges, the Mainichi said.
The detentions -- the first since 2010 involving Japanese on such charges -- come as relations remain clouded by disputes over islands and Tokyo's wartime history, despite close trade links.