Tensions remain high over the Japan-controlled, China-claimed Senkaku Islands in the East China Sea as Beijing continues to regularly send vessels into nearby waters, with Sunday marking 10 years since Tokyo brought most of the islets under state control.

The Senkakus, which China calls Diaoyu, have been a thorny and long-running issue in bilateral relations. Despite repeated protests from Tokyo, Beijing, which has also aggressively asserted territorial claims in the South China Sea, continues to send vessels to waters around the islands in a bid to shift the status quo.

A Chinese diplomatic source indicated Beijing's frequent dispatch of vessels to waters near the uninhabited Senkakus has eroded Japan's effective control, saying China is close to having "the upper hand" in the bilateral row so Beijing does not need to escalate its actions.

Since the Japanese government purchased most of the Senkaku Islands from a private owner on Sept. 11, 2012, Tokyo has observed 332 cases of official Chinese vessels entering Japanese territorial waters in total as of late August, including 19 cases this year.

Before the purchase, there had been almost no instances in which Chinese ships entered the Japanese territorial waters near the islands, according to the Japan Coast Guard.

Chinese vessels "always stay (in the disputed area) unless waters get rough," a Japan Coast Guard official said.

Since 2020, Chinese vessels have been spotted in the sea near the Senkakus on around 330 days each year, with a record 157 consecutive days in which the so-called contiguous zone outside Japanese waters was breached between February and July last year.

In July this year, two China Coast Guard vessels remained in Japanese territorial waters for a record 64 consecutive hours as they tracked a Japanese fishing boat.

Undated photo shows a Chinese Navy frigate sailing just outside Japanese territorial waters around the Senkaku Islands in the East China Sea.  (Photo courtesy of the Japanese Defense Ministry)(Kyodo)

Free passage of a coastal state's territorial waters is guaranteed under international law so long as it is not prejudicial to the peace, good order or security of the other state.

But Japanese maritime authorities warn Chinese vessels against entering its territorial waters as they believe Beijing dispatches the ships to areas near the Senkaku Islands to create a new status quo.

In the summer of 2016, up to 300 Chinese fishing vessels came close to the Senkaku Islands, with some repeatedly entering Japanese territorial waters.

Patrol boats from the 11th Regional Coast Guard Headquarters based in Naha, Okinawa Prefecture, protect Japanese fishing vessels when Chinese ships approach them in waters near the Senkakus.

The Japanese law-enforcement body monitors the situation around the clock and urges China Coast Guard ships using an electronic sign to leave the Japanese territorial waters if they enter. It also works with the Maritime Self-Defense Force, which mobilizes destroyers and patrol aircraft on the high seas.

The China Coast Guard, established in 2013 in a realignment of the country's maritime law-enforcement institutions, is now under the Chinese People's Armed Police Force, which is supervised by the Central Military Commission.

In February last year, Beijing implemented a new law that explicitly allows the China Coast Guard to use weapons against foreign ships it sees as illegally entering its waters.

China has also been stepping up its criticism against Japan over the territorial row, claiming in a digital exhibition on the disputed islands that Japan "stole" them. Opened in 2020, the virtual museum is now viewable in Chinese, English, Japanese, French, German, Russian, Spanish and Arabic.

Atsushi Toyama, a former senior Japan Coast Guard official who dealt with the 2016 entry into Japanese territorial waters of a large number of Chinese vessels, told Kyodo News that he thinks the 2012 purchase of the Senkakus by the Japanese government gave China "an excuse" to constantly send vessels to the sea area.

He said the Japan Coast Guard has protected the Senkakus while trying to avoid any military clash in the waters.

"I believe some people (in Japan) have been frustrated with the continued presence of Chinese vessels in the sea area. But if we resort to provocative action, it would only allow (Beijing) to take advantage of the situation," Toyama said.

To resolve the territorial row, he called for a multilayered approach based on diplomacy, politics and stronger cooperation between the Self-Defense Forces and the Japan Coast Guard.

Related coverage:

Japan concerned about China's activities around Senkakus: spokesman

PM Kishida eyes attending event on Japan-China ties' 50th anniversary

110 tril. yen sought for Japan FY 2023 budget, defense costs to rise

The following is a chronology of major events related to the Senkaku Islands in the East China Sea that have been a thorny issue in relations between Japan and China.

1895 -- Japan incorporates the Senkaku Islands into Okinawa Prefecture.

1932 -- The government sells four of the eight isles to a Japanese citizen.

1952 -- The Senkakus are officially placed under the administration of the United States in accordance with the San Francisco Peace Treaty.

1971 -- China and Taiwan officially assert territorial sovereignty over the islands for the first time.

May 1972 -- The United States returns to Japan the Nansei Islands, including the Senkakus.

September -- Japan and China normalize diplomatic relations.

1992 -- China establishes a territorial law claiming the Senkakus, which it calls Diaoyu.

2010 -- A Chinese fishing boat collides with Japan Coast Guard vessels off the Senkakus.

April 2012 -- Tokyo Gov. Shintaro Ishihara says the metropolitan government plans to purchase the privately owned part of the islands.

September -- The Japanese government acquires three of the four islets under private ownership, triggering repeated intrusions into Japanese waters by Chinese government vessels.

December -- A Chinese government plane enters Japanese airspace over the Senkakus for the first time.

January 2013 -- A Chinese warship locks weapon-guiding radar onto a Japan Maritime Self-Defense Force vessel near the Senkakus.

July -- The China Coast Guard is launched.

2014 -- A Japan-U.S. joint statement stipulates Washington's commitment under security pact to defending all territories under Japan's administration, including the Senkakus.

2016 -- The Japan Coast Guard deploys 12 large patrol vessels to be exclusively used for boosting security around the Senkakus.

2018 -- The China Coast Guard is placed under the Chinese People's Armed Police Force supervised by the country's Central Military Commission.

2021 -- China implements a new law that explicitly allows the China Coast Guard to use weapons against foreign ships it sees as illegally entering the Asian country's waters.