Prime Minister Shinzo Abe has pressed China's Vice President Wang Qishan over the detention of a Japanese man in China

Prime Minister Shinzo Abe on Wednesday pressed China's visiting vice president over the case of a Japanese professor detained by Beijing reportedly on allegations of spying.

Tokyo confirmed this week a Japanese man in his 40s has been held by Chinese authorities since September on suspicion of violating Chinese laws, without specifying the details.

Japanese media have identified him as a professor from Hokkaido University who is being detained on suspicion of spying.

Abe "strongly demanded a positive response from China regarding the detention of a Japanese national" when he met Wang Qishan on Wednesday, Chief Cabinet Secretary Yoshihide Suga told reporters.

He gave no further details on the exchange.

The man, who has not been named, worked previously for the National Institute for Defense Studies in the defence ministry and the Japanese foreign ministry, according to local media reports.

On Monday, Chinese foreign ministry spokeswoman Hua Chunying said she did not know the details of the case, but that China "has always handled foreign nationals suspected of breaking China's law, in accordance with the law".

Hua said the detention was a "one-off case".

"We hope that the Japanese side can remind its citizens to respect China's laws and regulations and avoid engaging in illegal activities in China," she added.

Beijing has faced accusations of using detentions of foreigners as a political tool, and observers have called it "hostage diplomacy".

In 2017, China detained six Japanese citizens for alleged "illegal activities."

Since 2015, at least 13 Japanese citizens -- all civilians -- have been detained in China on various charges including espionage, Japan's Kyodo News and the Asahi Shimbun reported.

Tokyo's ties with Beijing have been at times strained by rows over history and territorial disputes but have been improving recently, with President Xi Jinping expected to visit Japan early next year.