Sources say a Japanese man was detained by Chinese intelligence authorities last year. He was later indicted.
Japan's Foreign Ministry and others say the man is in his 40s and an employee at major trading house Itochu.
They say he was taken into custody in the southern city of Guangzhou last February. Details of his charges are not available.
The man was reportedly indicted in June and his closed-door trial began in July.
Itochu is known for its close business relationship with China.
A former chairman of the firm, Uichiro Niwa, served as Japan's ambassador to China.
Chinese Foreign Ministry spokesperson Hua Chunying said at a news conference on Thursday that the ministry has no information on the matter.
Since 2015, eight other Japanese nationals have been indicted in China on charges such as espionage. Four of them were handed down prison terms at their first trials.
Itochu says it is seeking to confirm the situation, including the reason for the employee's detention.
Japan's Chief Cabinet Secretary Yoshihide Suga said at a news conference on Thursday that a Japanese man in his 40s was detained and indicted in China last year.
Asked about the charges, Suga declined to give further details, citing the nature of the matter.