China's navy said Tokyo's claim was "completely inconsistent with the facts" and told Japan to "immediately stop slandering and smearing".

Relations between Tokyo and Beijing have soured following remarks by new Japanese Prime Minister Sanae Takaichi suggesting that Tokyo could intervene militarily in any attack on Taiwan.

Chinese J-15 fighter jets twice locked radar on Japanese fighter jets on Saturday, without causing damage or injuries, Japan's defence ministry said.

Fighter jets use their radar for fire control to identify targets as well as for search and rescue operations.

Defence Minister Shinjiro Koizumi said the incident was "dangerous and extremely regrettable", adding that Japan had lodged "a strong protest" with China.

Beijing's foreign ministry said it rejected that protest, and had lodged its own counter-protest, according to state news agency Xinhua.

A foreign ministry spokesperson, cited by Xinhua, urged Japan to "immediately stop its dangerous moves of harassing China's normal military exercise and training".

- 'Deeply concerned' -

The two countries have a long-running territorial dispute over the Senkaku Islands, known as the Diaoyu in China.

The tiny, uninhabited islands lie between Okinawa and Taiwan, the much larger self-ruled island that China also claims.

Beijing summoned Tokyo's ambassador following Takaichi's comments last month.

Tokyo is deepening cooperation with US allies in the Asia-Pacific region, where several countries have territorial disputes with China.

Beijing, for instance, claims nearly all of the South China Sea, and has been asserting control more strongly in parts of the strategic waterway despite an international ruling that its claim has no legal basis.

The incident at the weekend came as Australia's Defence Minister Richard Marles was visiting Japan.

Marles said he was "deeply concerned by the actions of China in the last 24 hours", following a meeting with his Japanese counterpart.

He said Canberra had "stabilised" its relationship with China by "acting in a clear, consistent, calm and sensible way".

"We will seek to work together with China where we can, but we will disagree where we must," he said in response to a question about supply chains.

Marles also visited Mitsubishi's shipyard in Nagasaki, months after Canberra signed a major $6 billion deal to buy 11 advanced warships from the Japanese firm.