TOKYO, Oct 23 (Reuters) - Chinese authorities detained a local employee of a Japanese trading firm this year, according to The Nikkei newspaper, the latest report of a spate of raids on foreign companies and detentions of their staff in China.

The report, citing sources and released late Sunday, did not identify the firm or the staff member, only saying the person was a Chinese national who oversaw rare metals at the company. The reason for arrest was unknown, the report said.

China's foreign ministry did not immediately respond to a request for comment.

Hirokazu Matsuno, the top Japanese government spokesperson, said Tokyo is monitoring the situation closely.

"It's essential to ensure transparency of law enforcement and judicial processes, and a predictable and fair business environment in China to promote economic and human exchanges between Japan and China," Matsuno, the chief cabinet secretary, told reporters.

The detention took place back in March about the same time as a raid on U.S. consultancy Mintz's Beijing office in which several of that company's local staff were detained.

That incident, as well as a raid on U.S. management consultancy Bain & Co, the arrest of an executive from Japan's Astellas Pharma and travel restrictions imposed on a senior Nomura banker, have sent chills through China's foreign business community. (Reporting by John Geddie; Additional reporting by Satoshi Sugiyama in Tokyo and Ryan Woo in Beijing; Editing by Gerry Doyle)