Japan's prime minister vowed Tuesday to "expel by force" any Chinese landing on islands at the centre of a territorial row, after eight Chinese government vessels sailed into the disputed waters.
The latest clash over the archipelago upped the stakes in a tense diplomatic battle as nearly 170 Japanese lawmakers visited the controversial Yasukuni war shrine in central Tokyo, seen as a potent symbol of Japan's imperialist past, riling its neighbours China and South Korea.
Tokyo summoned the Chinese ambassador to Japan after the state-owned Chinese ships entered its territorial waters while Beijing called the shrine visit an "attempt to deny Japan's history of aggression".
The flotilla is the biggest to sail into the disputed waters in a single day since Tokyo nationalised part of the island chain in September.
The islands are surrounded by rich fishing grounds and are believed to harbour vast natural resources below the seabed.
Prime Minister Shinzo Abe vowed to "expel by force" any Chinese landing on the islands in the East China Sea, and promised "decisive action".
"We would never allow a landing," Abe told parliament in response to questions from lawmakers, adding: "It would be natural for us to expel by force if (the Chinese) were to make a landing," he said.
Chinese ships have frequently sailed around the five Tokyo-controlled islands in recent months sparking diplomatic clashes.
The Chinese maritime surveillance ships entered the 12-nautical-mile zone off the islands, which China calls Diaoyu and Japan calls the Senkaku, around 8:00 am (2300 GMT Monday), the Japan Coast Guard said.
The eight vessels left by about 7:15 pm, Jiji Press news agency reported, quoting the regional coast guard headquarters.
"It is extremely deplorable and unacceptable that Chinese government ships are repeatedly entering Japanese territorial waters," Japan's Chief Cabinet Secretary Yoshihide Suga said.
A group of Japanese nationalists said it had sent nine ships to the area around the islands, which are also claimed by Taiwan.
The United States, which has a military alliance with Japan, called for calm.
"We do urge all parties to avoid actions that could raise tensions or result in miscalculations that would undermine peace, security and economic growth in that vital part of the world," State Department spokesman Patrick Ventrell said.
In a separate territorial row, relations between Tokyo and South Korea have also been strained by a dispute over a Seoul-controlled chain of islets in the Sea of Japan (East Sea).
Seoul on Monday shelved a planned trip by Foreign Minister Yun Byung-Se to Tokyo after two Japanese cabinet ministers visited the shrine over the weekend.
The shrine is seen by Japan's neighbours as a symbol of its wartime aggression as it honours 2.5 million war dead, including 14 leading war criminals.
Beijing also protested the visits.
"No matter in what capacity or form Japanese leaders visit Yasukuni Shrine, in essence it is an attempt to deny Japan's history of aggression through militarism," Foreign Ministry spokeswoman Hua Chunying told reporters on Tuesday.
"How Japan views history and deals with the Yasakuni Shrine is an important benchmark for its Asian neighbours and the international community to observe and understand what role Japan will play in the future."
South Korea meanwhile pressed Tokyo to "think hard" about the shrine visits.
"The Yasukuni shrine is a place that glorifies war and enshrines war criminals," foreign ministry spokesman Cho Tai-Young told reporters in Seoul.
Upper house member of parliament Toshiei Mizuochi confirmed that 168 Japanese lawmakers visited the shrine on Tuesday morning -- the annual visit usually draws a far smaller number of legislators.
Suga, who is the Japanese government's top spokesman, brushed off anger over the issue, saying on Tuesday it was a personal matter for lawmakers and Tokyo would not interfere.
"A visit to the Yasukuni is the matter of beliefs, and Japan ensures freedom of faith," he said.
Japan's Deputy Prime Minister Taro Aso and Keiji Furuya, the chief of the National Public Safety Commission, separately visited the shrine on Sunday, while Internal Affairs Minister Yoshitaka Shindo also visited at the weekend.
Japan's premier did not make a pilgrimage but paid for equipment made of wood and fabric, bearing his name and title, which was used to decorate an altar.