Four Chinese corvettes approached the territorial waters of Japan, while one of them crossed into the Japanese area near the disputed Senkaku Islands, according to the NHK broadcaster.
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The crisis response headquarters will collect information about the incident and monitor the situation, the news outlet added.
The Senkaku archipelago dispute escalated in 2012, when the Japanese government bought three of the five islands from a private Japanese owner.
In May 2018, China and Japan agreed to launch a mechanism, envisaging the establishment of a communications line that would be used to avoid potential armed clashes between the aircraft and warships of the two states in the East China Sea.