Japan says it has protested the "illegal act" with Chinese authorities Tokyo will take "all possible measures to ensure security," Noda says Tokyo (CNN) -- Six Chinese maritime surveillance ships entered waters around a group of islands at the center of a heated territorial dispute between Tokyo and Beijing, ignoring warnings from the Japanese authorities amid escalating tensions in the region. The Chinese ships arrived near the uninhabited islands -- which Japan calls Senkaku and China calls Diaoyu -- on Friday morning and began patrols and "law enforcement," China's state-run news agency Xinhua reported. The long-running argument over who has sovereignty has resulted in occasionally violent acts of public protest. Japanese Chief Cabinet Secretary Osamu Fujimura said Japan would intensify its own patrols of the area in response to what he described as an "unprecedented scale of invasion" of Japanese waters. Tokyo has protested the "inappropriate, illegal act" to the Chinese authorities, Fujimura said, calling for the ships to leave the area. Prime Minister Yoshihiko Noda said Japan would "take all possible measures to ensure security" around the islands. Japanese ships and helicopters are continuing their own patrols of the area, he said. The purpose of the patrols is "to demonstrate China's jurisdiction over the Diaoyu Islands and its affiliated islets and ensure the country's maritime interests," Xinhua reported Friday, citing a government statement. This week, China announced what it said were the boundaries of its territorial waters around the islands to back up its claim sovereignty. It said it had filed a copy of the announcement with U.N. Secretary General Ban Ki-moon on Thursday to comply with international law. But Fujimura insisted Friday that the islands are an "integral part of Japanese territory" under international law, highlighting how directly opposed the two sides are. CNN's Junko Ogura reported from Tokyo and Jethro Mullen from Hong Kong.