Chinese and Russian warplanes on Tuesday conducted joint air patrols over the Sea of Japan, the East China Sea and the West Pacific Ocean as the leaders of Quad held their in-person summit in Tokyo, in an apparent attempt to send a message of unity between Beijing and Moscow.

The air forces of China and Russia conducted routine joint strategic air patrols over the Sea of Japan, the East China Sea and the West Pacific Ocean on Tuesday, in line with the annual military cooperation plan between the two armies, the Chinese Ministry of Defence said here in a brief announcement.

The second in-person Quad summit was attended by Prime Minister Narendra Modi, US President Joe Biden, Japanese Prime Minister Fumio Kishida and the new Australian Prime Minister Anthony Albanese.

Media reports from Tokyo quoted Japanese Defence Minister Nobuo Kishi as telling the media that Japan had expressed grave concerns over the joint sorties by the Russian and Chinese military flights when the leaders of the Quad alliance consisting of the US, India, Japan and Australia held the second in-person summit on Tuesday.

Two Chinese bombers joined two Russian bombers in the Sea of Japan and made a joint flight to the East China Sea, Kishi said, adding that Japan has taken up the issue with both the countries through diplomatic channels.

China and Russia have conducted annual military drills in the Pacific in the past.

However, to hold such a drill on the day of the Quad summit was seen here as an attempt by Beijing and Moscow to send a message of unity and closeness in the backdrop of growing international criticism against Russia over its offensive against Ukraine and China's firm backing to it.

Separately in Beijing, the Chinese Foreign Ministry asserted that China-Russia relations have withstood the new test of the changing international landscape and were moving forward in the right direction.

When asked to respond to Russian Foreign Minister Sergey Lavrov's remarks that Russia will continue to develop friendly relations with China and the ties will grow faster, especially when the West is taking the position of a dictator , Chinese Foreign Ministry spokesman Wang Wenbin told a media briefing here that the cooperation is driven by strong internal dynamics.

China and Russia are each other's biggest neighbours, most important close neighbours and comprehensive strategic partners of coordination, Wang said on Tuesday.

China-Russia relations have withstood the new test of the changing international landscape and are moving forward in the right direction. The China-Russia cooperation is driven by strong internal dynamics and is valued for its independence. It is not targeted at any third party and will not be affected by others, he stressed.

As permanent members of the UN Security Council and important members of multilateral mechanisms such as BRICS, the Shanghai Cooperation Organisation and the G-20, China and Russia will remain committed to promoting a multi-polar world and greater democracy in international relations, upholding true multilateralism and opposing hegemonic behaviours and bloc confrontation in international relations, he added.

Russia's Foreign Minister Sergey Lavrov said on Monday that economic cooperation between Russia and China will gain momentum in the near future as the West "holds a dictator's position," Russian state-run news agency Tass reported.

He pointed out that relations between Moscow and Beijing are based on doctrinal documents that "characterise [these] contacts as the strategic partnership and the multi-aspect interaction."

Lavrov also noted that the Russian Federation has "a long border with the People's Republic of China and common interests in defending principles of justice and the multi-polar world order in international affairs.