China first claimed territorial rights over the Senkaku Islands in Okinawa Prefecture in 1971.
Two years earlier, the then UN Economic Commission for Asia and the Far East compiled a report identifying possible undersea oil reserves near the islands.
The report is believed to have spurred China to assert its claim over the islands. In 1992 China passed the "territorial water law" and unilaterally added the islands to its territories.
In 2012 it was discovered that then Tokyo Gov. Shintaro Ishihara had been negotiating the purchase of three of the Senkakus with their owner.
The then Democratic Party of Japan-led administration of Yoshihiko Noda feared the islands would become "metropolitan estates" under Ishihara, a hard-liner against China. Before the purchase by the metropolitan government was carried out, the central government bought the islands and nationalised them on Sept. 11, 2012.
The Chinese government reacted fiercely against Japan's action. Since then it has taken provocative steps, such as dispatching China Coast Guard ships into Japan's territorial waters.
Within the Japan Coast Guard, the 11th Regional Coast Guard Headquarters based in Naha is in charge of the sea around the Senkaku Islands. It has seven large patrol ships of 1,000 tons or larger.
However, seven ships are insufficient to cope with Chinese vessels in the area and patrol ships from other regional headquarters have been dispatched to Okinawa Prefecture.