Japan lodged a strong protest with China on Tuesday after four Chinese government ships entered Japanese territorial waters around a chain of disputed islands in the East China Sea on the previous day. Vice Foreign Minister, Akitaka Saiki, summoned Chinese Ambassador to Japan, Cheng Yonghua, over the intrusion and strongly urged China to prevent a recurrence, according to the ministry. It was the first time that conservative Prime Minister Shinzo Abe's government, launched on December 26, to protest against China's dispatching of ships to Japanese territorial waters. The Japan Coast Guard said it spotted four Chinese maritime surveillance ships on Monday for the first time this year in sovereign waters off the Japan-administered Senkaku Islands, which are also claimed by China and Taiwan. The coast guard warned the Chinese ships to leave the waters, but the ships remained in the waters for more than 13 hours until they left shortly after midnight. The small chain of uninhabited rocky islands, known as Diaoyu in China and Tiaoyutai in Taiwan, lie in rich fishing grounds and waters thought to contain large deposits of oil and natural gas. Relations between the world's second and third-largest economies have sharply deteriorated since Tokyo's nationalization of three of the five major islands in September last year through purchase from a private Japanese owner. (