Three Chinese government ships entered waters around disputed islands controlled by Tokyo on Thursday, Japan's coastguard said.
The Chinese maritime surveillance vessels were spotted in the 12-nautical-mile zone off the Senkaku islands, which China calls the Diaoyus, in the East China Sea shortly before 9:30 am (0030 GMT), the coastguard said.
It marks the latest in a long line of stand-offs between official ships from both sides as Beijing and Tokyo jostle over ownership of the strategically important and resource-rich islands.
A long-simmering territorial row that dates back four decades blistered in September when Tokyo nationalised three islands in the chain, in what it said was a mere administrative change of ownership.
The central government's move was intended to pre-empt a purchase by the Tokyo city government led by nationalist governor Shintaro Ishihara at the time.
Tokyo's move prompted angry anti-Japan demonstrations across China, which has intensified claims to the islands it says should have been "returned" after World War II.