Japan scrambles fighter jets after Russian and Chinese warplanes near its airspace in first joint military exercise since Ukraine invasion - as President Biden visits Tokyo 

• Japan conveyed 'grave concerns' to diplomats after two Chinese military aircrafts and four Russian warplanes entered its air defence identification zone
• Tokyo was hosting the leaders of the Quad countries, including the US
• The joint military exercise was the first held between China and Russia since war in Ukraine broke out on February 24, which the quad countries condemned
• Jets also came close to violating South Korean airspace in a separate incident 

Japan scrambled jets after two Chinese military aircrafts and four Russian warplanes entered its air defence identification zone on Tuesday on the same day President Joe Biden landed in Tokyo.

It was the first joint military exercise held between China and Russia since the war in Ukraine broke out on February 24.

Tokyo is hosting the leaders of the Quad countries including the United States, India and Australia. 

Japan conveyed 'grave concerns' to both Russia and China through diplomatic channels, said Japanese defence minister Nobuo Kishi at a news conference that was broadcast online.

He characterised the incident as a likely provocation by both Beijing and Moscow on a day when US President Joe Biden, Indian Prime Minister Narendra Modi and Australia's newly elected leader, Anthony Albanese, were meeting in Tokyo.

'We believe the fact that this action was taken during the Quad summit makes it more provocative than in the past,' he said, adding it was the fourth such incident since November.

Two Chinese warplanes flew over the Sea of Japan from the East China Sea and were then joined by two Russian warplanes for a flight together toward the East China Sea, Kishi said.

Russian and Chinese jets had already entered South Korea's air defence identification zone earlier in the day. 

Later, the two Chinese warplanes were replaced by another pair believed to be Chinese, which then flew with the Russians on a long flight toward the Pacific Ocean, he said.

A Russian reconnaissance plane also flew over the open sea from the northern island of Hokkaido to the Noto peninsula on Japan's main island, he said.

None of the aircraft entered into Japan's airspace, he said.

Russia and China both confirmed they conducted a joint patrol. Russia's defence ministry said the patrol lasted 13 hours over the Japanese and East China seas.

The Japanese government had been tracking the military exercise in northeast Asia, said The New York Times.

The exercise was part of an 'annual military cooperation plan', China's defence ministry said.

In a separate incident, the South Korea's military said it scrambled fighter jets after at least four Chinese and four Russian warplanes entered its air defence zone on Tuesday.

The Russian and Chinese aircraft entered and left the Korea Air Defence Identification Zone (Korea ADIZ) in the Sea of Japan, several times through the day, according to South Korea´s Joint Chiefs of Staff (JCS).

The aircraft, which included fighter jets and bombers from each side, did not violate South Korea's airspace, the JCS added.

The South Korean military deployed air force fighters to 'implement tactical measures' to brace for a potential contingency, it said.

Unlike airspace, an ADIZ is usually an area where countries may unilaterally demand that foreign aircraft take special steps to identify themselves, with no international laws governing ADIZs.

Moscow does not recognise the Korea ADIZ, while Beijing said the area is not territorial airspace and all countries should enjoy freedom of movement there.

In 2019, South Korean warplanes fired hundreds of warning shots toward Russian military aircraft when they entered South Korean airspace during a joint air patrol with China.

The four leaders of the Quad - an informal grouping led by Washington - on Tuesday stressed their determination to ensure a free and open Indo-Pacific region in the face of an increasingly assertive China. 

A joint statement by the Quad bloc avoided any direct mention of China's growing military power in the region, but left little doubt about where its concerns lie.

The carefully worded document also made reference to the conflict in Ukraine, but without offering any joint position on the Russian invasion, which India has pointedly declined to condemn.

The Quad's other members have been less coy about their view that a strong response to Russia's war is needed, one that would deter other countries, including China.

'As Russia's invasion of Ukraine is shaking the fundamental principles of the international order... (we) confirmed that unilateral attempts to change the status quo by force will never be tolerated anywhere, particularly in the Indo-Pacific region,' Japan's Prime Minister Fumio Kishida said, using another term for the Asia-Pacific.

The group's statement made no mention of Russia, or China, but inveighed against a range of activities that Beijing has regularly been accused of in the region.

'We strongly oppose any coercive, provocative or unilateral actions that seek to change the status quo and increase tensions in the area, such as the militarisation of disputed features, the dangerous use of coast guard vessels and maritime militia and efforts to disrupt other countries' offshore resource exploitation activities,' it said.

The Quad nations are attempting to build their loose grouping into a more substantive counterweight to China's rising military and economic power, despite their differences.

They unveiled plans to invest at least $50billion into regional infrastructure projects over the next five years, and a maritime monitoring initiative seen as intended to bolster surveillance of Chinese activities.

The moves come with worries over recent efforts by China to build ties with Pacific nations including the Solomon Islands, which signed a security pact with Beijing last month.

China's foreign minister will this week kick off a visit to a host of Pacific nations including the Solomons, Papua New Guinea, Fiji and Kiribati as well as holding video calls with Micronesia and the Cook Islands, Beijing confirmed Tuesday.

Kishida urged Quad members to 'listen carefully' to regional neighbours, including the Pacific islands, while Australia's newly elected Prime Minister Anthony Albanese said the bloc needed to 'push our shared values in the region at a time when China was clearly seeking to exert more influence'.

The Quad met a day after US President Joe Biden raised eyebrows and the regional temperature by saying Washington was ready to intervene militarily to defend Taiwan against any Chinese attack.

He insisted Tuesday that his comments did not mean a change to Washington's longstanding 'strategic ambiguity' on how it might respond to a Chinese invasion, prompting another fierce response from Beijing.

Foreign ministry spokesman Wang Wenbin accused Washington of playing 'word games' on Taiwan and warned of an 'unbearable cost' if the United States 'carries on down the wrong path'.

If Biden was keen to avoid being seen as changing policy on Tuesday, he left little doubt about where the Quad's focus lies.

'This is about democracies versus autocracies, and we have to make sure we deliver,' Biden said as the summit began.

Among the regional concerns are increased Chinese sorties, naval exercises and encroachments by fishing vessels that are viewed as probing regional defences and red lines.

The bloc said its new maritime monitoring programme would 'promote stability and prosperity in our seas and oceans', again avoiding pointing the finger at Beijing while referencing illegal fishing - an accusation frequently levelled at China.