The incident further soured relations between Beijing and Tokyo that have suffered since comments by Japanese Prime Minister Sanae Takaichi about the self-ruled island of Taiwan.

Japan's national broadcaster NHK said the man had entered the heavily guarded embassy grounds on Tuesday morning and that a knife was later found at the scene.

NHK, citing unidentified investigation sources, said no one was hurt but added that the man was "believed to be a member of the Ground Self-Defense Force".

However, China's foreign ministry said the unidentified man had threatened to kill Chinese diplomats.

A ministry spokesman told a scheduled news conference in Beijing that the intruder had scaled the embassy walls before he was apprehended.

"The individual admitted that his actions were unlawful and threatened to kill Chinese diplomatic personnel 'in the name of God'," spokesman Lin Jian said.

"The Chinese side is deeply shocked by this incident and has lodged solemn representations and a strong protest with the Japanese side," he said.

Police in Tokyo could not be reached immediately for comment.

Japan's Defense Ministry said it was aware of the incident but declined to comment further, citing an ongoing investigation.

Lin demanded that Tokyo investigate the incident thoroughly.

Ties between Japan and China have deteriorated since Prime Minister Sanae Takaichi suggested in November that Japan might intervene militarily in any Chinese attempt to take Taiwan.

China, which regards the democratic island as part of its territory and has not ruled out force to annex it, was furious over the comments.

It summoned Tokyo's ambassador and warned Chinese citizens against visiting Japan, with tourism numbers plummeting since then.