Chinese coastguard ships entered the territorial waters of Japanese-controlled islands at the centre of a bitter row, Japan's coastguard said Friday, the first such incursion by the organisation.
Although Chinese government ships have been in and out of waters around the islands for many months, this is the first time they have ventured there since Beijing combined several agencies under the coastguard flag.
The move potentially further ramps up tensions around the Senkaku islands, which Beijing claims as the Diaoyus.
"We demanded they leave our territorial waters," an official at Japan's coastguard said.
The four vessels left the 12-nautical-mile band of waters around 1.30 pm (0430 GMT), approximately three hours after they arrived, he added.
Chinese media reported this week that a unified coastguard agency has gone into operation, integrating marine surveillance, the existing coastguard -- which came under the police -- fisheries law enforcement and Customs' anti-smuggling maritime police.
Chinese academics were reported as saying that the move would mean more armed ships.