Chinese Navy
Chinese navy sailors stand in formation as they attend a send-off ceremony before departing for the Rim of the Pacific exercise, at a military port in Sanya, Hainan province, China, June 9, 2014. Reuters

Japan alleged Monday that China violated the international maritime law when three Chinese patrol vessels trespassed into sovereign Japanese waters. The alleged incursion occurred in the area off Uotsuri Island in the Senkaku Islands in the East China Sea shortly after 10:30 a.m. Monday, according to NHK.

The Chinese patrol boats left Japanese waters after about an hour. Monday’s incursion was the 36th such incident this year, the last taking place on Dec. 11.

Part of an ongoing feud, territorial claims over Senkaku Islands by China and Taiwan have consistently been contested by Japan which says the islands are an inherent part of its territory. Regarding Monday’s incident, the Japanese Foreign Ministry lodged a protest with the Chinese embassy in Tokyo, NHK reported.

In another separate but related incident, a Chinese aircraft carrier's voyage in the Pacific has also become a cause of concern for Japan, and a government spokesman said the country is monitoring the situation closely.

Japan’s Chief Cabinet Secretary Yoshihide Suga said the country aims to take all steps for warning and surveillance activity in the area, according to Reuters. This is the first instance of a Chinese aircraft carrier being spotted in the Pacific, according to the NHK which cited Japan’s Maritime Self-Defense Force officials.

Meanwhile, Taiwan also expressed concerns over the aircraft carrier, which it said was accompanied by five other vessels as it passed through waters south of Taiwan via the Bashi Channel, between Taiwan and the Philippines as it went southwest.

"Staying vigilant and flexible has always been the normal method of maintaining airspace security," Taiwan's defense ministry spokesman Chen Chung-chi said, adding the ministry was continuing to "monitor" the situation.

However, Chinese state media reported the deployment of the vessel was part of routine training, according to BBC. "A Chinese navy formation, including the aircraft carrier Liaoning, headed towards the West Pacific on Saturday for scheduled blue-water training," Chinese state news agency Xinhua reported, quoting navy spokesperson Liang Yang.

But despite China downplaying the issue, the move assumes significance as diplomatic relations between China and Taiwan recently soured after U.S. President-elect Donald Trump broke diplomatic protocol and spoke with Taiwan President Tsai Ing-wen by telephone. He also questioned the need for the U.S. to follow its accepted doctrine of the "one-China" policy.

The Chinese Communist Party forced the Nationalist Party (KMT) to retreat to Taiwan in 1949 and since then, China continues to view the territory suspiciously and has said it can be retaken by force if necessary. China also cut off communications with Taiwan in June after the ruling pro-independence Democratic Progressive Party declined to acknowledge the "one-China" policy.

Earlier this week, Japan unveiled a record defense budget of 5.13 trillion yen ($43.6 billion), aimed at strengthening security and boosting its naval power amid rising tensions with China and North Korea.