Nobuo Kishi said the government had expressed "grave concerns" to Russia and China over the flights, which took place while leaders from the United States, India, Australia and Japan held talks on regional security.

The planes did not breach territorial airspace, the defence ministry told AFP, and it was the fourth time since November that long-distance joint flights by Russia and China had been spotted near Japan.

"Two Chinese bombers joined two Russian bombers in the Sea of Japan and made a joint flight to the East China Sea," Kishi told reporters.

"After that, a total of four aircraft, two presumed (new) Chinese bombers -- which replaced the two Chinese bombers -- and two Russian bombers, conducted a joint flight from the East China Sea to the Pacific Ocean."

He said a Russian intelligence-gathering aircraft also flew off northern Hokkaido to the Noto Peninsula in central Japan on Tuesday, calling the moves especially "provocative" given the summit in Tokyo.

Beijing confirmed the flights in a short statement, and said it was in line with the Chinese and Russian "annual military cooperation plan".

"On May 24, both countries' air forces organised and carried out a routine joint strategic mid-air patrol in the airspace above the Sea of Japan, East China Sea and Western Pacific maritime areas," a statement from the ministry of defence said.

The Quad leaders on Tuesday warned against attempts to "change the status quo by force", although they avoided direct references to Russia or China in a joint statement.

Their statement referred to the war in Ukraine, however, and warned against a range of activities which Beijing has regularly been accused of in the region.

Kishi said Japan had "communicated through diplomatic routes our grave concerns from the perspective of our country's and the region's security".

"As the international community responds to Russia's aggression against Ukraine, the fact that China took such action in collaboration with Russia, which is the aggressor, is cause for concern. It cannot be overlooked."

Japan, which has volatile ties and border disputes with its neighbours China, Russia and South Korea, routinely sends jets to defend its air borders.

The country scrambled military jets 1,004 times in the year to March, the second-highest count on record, according to the defence ministry.

Most were to counter approaching Chinese aircraft, although many of the rest involved Russian aircraft.