The ships were in the disputed territory Friday to collect evidence of Japanese ships' and planes' infringement on Chinese sovereignty over what China calls the Diaoyu islands and Japan calls the Senkaku islands, Xinhua reported.
Japanese coast guard ships issued warnings to the Chinese vessels and the Chinese demanded the coast guard ships leave the area, a statement from the State Oceanic Administration in China said.
The move came a week after Japanese defense radar failed to detect Chinese aircraft entering airspace over the disputed islands, CNN reported.
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