Japan has lodged a formal protest with China after a Chinese plane reportedly flew close to islands claimed by both countries.
For the first time, Tokyo accused the Chinese of violating Japanese airspace in another escalation in the territorial dispute.
Japan says the Chinese maritime surveillance plane was spotted late on Thursday morning local time, much closer than usual to one of the islands.
Japan controls the islands it calls Senkaku and Beijing calls Diaoyu in the East China Sea. The area has important shipping lanes, fishing grounds and it is thought there might be oil.
“It is extremely deplorable that China’s official airplane invaded Japan’s territorial airspace today, on top of their (ships’) intrusion of territorial waters for the last three days in a row, despite our repeated warnings,” said Osamu Fujimura, the Japanese government’s Chief Cabinet Secretary.
The Japanese air force scrambled fighter jets in response. Japanese ships have been patrolling the area, on the lookout for more Chinese boats.