Japan has summoned the Chinese ambassador in protest over a flotilla of Chinese government ships that entered territorial waters near a disputed island chain.
Japan's foreign ministry said on Tuesday it had called in the envoy after eight Chinese vessels entered waters near the Senkaku islands, which China calls Diaoyu, the most in a single day since Tokyo nationalised part of the archipelago in September.
The Chinese boats drove out a flotilla of 10 boats carrying about 80 Japanese activists from the nationalist Ganbare Nippon ("Stand Firm, Japan") group, which sailed into waters around the islets early on Tuesday.
They then began to withdraw from the area on the orders of Japanese Coast Guard patrol ships, when Chinese government surveillance ships came nearby.
"Our latest intelligence indicates that a large number of Chinese vessels have entered Japanese territorial waters," an unidentified coast guard member told the activists.
Japanese chief cabinet secretary Yoshihide Suga on Tuesday confirmed the incident. "Today there has been eight Chinese maritime surveillance vessels that have entered the Senkaku island area around Uotsuri Jima," he said.
China said the trip by Ganbare Nippon was "illegal" and "troublemaking," and a foreign ministry spokesman said the government has lodged an official protest with Japan.
'Under our active control'
Japanese Coast Guard vessels then escorted some of the fishing boats back to the the port of Ishigaki, where they originally departed from.
Ganbare Nippon had said the purpose of their trip was to survey fishing grounds. Last August, about 10 activists from the group landed on one of the islets.
Japanese and Chinese patrol ships have been playing a cat-and-mouse game near the Japanese-controlled East China Sea islands, where China is seeking to assert its claim to sovereignty by sending ships into the disputed waters.
Japanese prime minister Shinzo Abe however said that it was Japan who was still fully in control of the island chain.
"The Senkaku islands are under our active control," he said when asked in parliament what he thought the status of the islands were.
"Since it has become the Abe government, we have made sure that if there an instance where there is an intrusion into our territory or it seems that there could be landing on the islands then we will deal will it strongly," Abe added.
The waters around the islets are rich fishing grounds and also have potentially huge oil and gas reserves.
The territorial dispute has escalated in recent months to the point where China and Japan have scrambled fighter jets while patrol ships shadow each other, raising fears that an unintended collision could lead to a broader clash.
A recent visit to the Yasukuni war shrine by Japanese politicians also added to the tensions between the two nations.
The shrine is seen by the Chinese as a glorification of Japan's wartime past as it honours fallen Japanese soldiers, including convicted war criminals.
China's foreign ministry lodged a diplomatic protest against the visit.