Chinese and Russian militaries conducted a joint aerial patrol on Tuesday, China's defence ministry said.
The patrol, part of the two countries' "annual military cooperation plan", took place over the Sea of Japan, East China Sea and the Western Pacific, the ministry said on its official website.
Russia's defence ministry said the patrol lasted 13 hours over the Japanese and East China seas.
The two countries had previously held such patrols in 2019, 2020 and 2021 but in the latter half of the year.
Russia has faced a barrage of sanctions from Western countries over its Feb 24 invasion of Ukraine, which it calls a "special military operation". Beijing has not condemned Russia's attack and does not call it an invasion, but has urged a negotiated solution.
Japan scrambled jets after Russian and Chinese warplanes neared its airspace on Tuesday, when Tokyo was hosting the leaders of the Quadrilateral Security Dialogue (Quad) grouping of countries that includes the United States, Defence Minister Nobuo Kishi said.
Tokyo conveyed "grave concerns" to both Russia and China through diplomatic channels, Kishi said 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.
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 Japan's airspace, he said.
Separately, South Korea's military said it scrambled fighters after at least four Chinese and four Russian warplanes entered its air defence zone on Tuesday.
It was not immediately clear if the two events were related or if any of the same warplanes were involved.
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.
