Tokyo: Four Chinese coastguard ships entered territorial waters near Tokyo-controlled islands at the centre of a bitter sovereignty row, Japan`s coastguard said.
The vessels entered the 12-nautical-mile band of waters at around 9:30 am local time (0030 GMT), the agency said, the latest in a series of incursions by Chinese government ships in recent months.
The incident Friday comes a week after the first entry by coastguard ships since Beijing combined several agencies under the coastguard flag last month, a development that observers said would involve the arming of more crew.
The island dispute has been cited as a potential flash point that may even lead to armed conflict between the Asian giants.
Observers say the presence of a large number of official vessels, some of them armed, increases the likelihood of a confrontation since a minor slip could quickly escalate.
Chinese media have reported that the unified coastguard agency integrates marine surveillance, the existing coastguard -- which came under the police -- fisheries law enforcement and customs` anti-smuggling maritime police.
Tensions have been building for months around the long-standing ownership dispute over the Senkaku islands, which Beijing claims as the Diaoyus.
In one of the most serious incidents of the row so far, Japan in March said a Chinese battleship locked its weapons-targeting radar on one of its vessels. Beijing denied the charge, accusing Tokyo of hyping the "China threat".
The disputed islands are located in rich fishing grounds are believed to harbour vast mineral reserves below their seabed.