Japan's top government spokesman has warned China against expanding its military activity in the skies over disputed East China Sea islands after eight Chinese warplanes flew near the area on Sunday.

Chief Cabinet Secretary Yoshihide Suga said Monday that Japan scrambled at least one fighter jet after the planes passed over the Miyako Strait, east of the Japan-controlled Senkaku islands, which China also claims and calls the Diaoyu.

Suga said the aircraft, believed to be two fighter jets, four bombers and two reconnaissance aircraft, did not violate Japanese airspace during a "long-distance roundtrip flight." He added that Japan would respond firmly to any violation of Japanese air space in the future.

Chinese media reports said the flights were part of a routine exercise involving about 40 military aircraft.