Japan expressed "serious concerns" on Wednesday after Chinese and Russian heavy bombers conducted rare joint flight operations around Japan the previous day as leaders of "the Quad" grouping met in Tokyo.

The Defense Ministry said it had scrambled fighter jets Tuesday in response to the operations that included a total of six Chinese and Russian bombers that made a joint flight through the Sea of Japan, East China Sea and into the Pacific Ocean. The warplanes did not enter Japanese territorial airspace.

Chief Cabinet Secretary Hirokazu Matsuno, the government's top spokesman, said during a news conference broadcast online on Wednesday that Tokyo could not overlook actions such as flights that "increase tensions in East Asia" when Moscow was continuing with its bloody war in Ukraine.