Japan on Thursday scrambled fighter jets after one Chinese state-owned aeroplane entered airspace over islands at the centre of a dispute between Tokyo and Beijing.
F-15 jets were mobilised after a Chinese maritime aircraft ventured over the Senkaku islands, which China calls the Diaoyus, just after 11 am (0200 GMT), Chief Cabinet Secretary Osamu Fujimura told reporters.
Chinese government ships have moved in and out of waters around the islands for more than two months, but this was the first time since the dispute flared that Tokyo has claimed any airborne incursion into what it says is Japanese territory.
Four maritime surveillance vessels were logged in waters around the islands earlier in the day, the coastguard said, adding it had ordered them to leave.
Such confrontations have become commonplace since Japan nationalised the East China Sea islands in September, a move it insisted amounted to nothing more than a change of ownership of what was already Japanese territory.
But Beijing reacted with fury, with observers saying the riots that erupted across China had at least tacit backing from the Communist Party government.
Thursday marks the 75th anniversary of the beginning of an episode known as the Nanjing Massacre, when Japanese Imperial Army troops entered the then-capital of China and embarked on an orgy of violence.