Taipei (AFP) - Taiwan told China on Monday to stop its “destructive unilateral actions” after more than 100 Chinese warplanes and nine navy ships were detected in areas around the self-ruled island.

Beijing claims Taiwan as its own territory to be seized one day, and has ramped up diplomatic and military pressure on Taipei in recent years.

In the 24 hours between the morning of September 17 and 18, the defence ministry said it had detected a total of 103 Chinese planes, and it described the number as a “recent high”.

In a statement, it said the sorties “posed severe challenges to the security across the Taiwan Strait and in the region.”

Beijing’s “continued military harassment can easily lead to a sharp escalation in tension and worsen regional security,” the ministry said, as it called on China to “immediately stop such destructive unilateral actions.”

Of the total number of warplanes detected, 40 crossed the so-called median line of the Taiwan Strait that separates the island from China, and entered its southwest and southeast air defence identification zone (ADIZ), the statement said.

China’s foreign ministry did not comment on the sorties, though its spokeswoman Mao Ning reaffirmed Beijing’s position that Taiwan belongs to China.

“What I would like to tell you is that Taiwan is part of China’s territory, and the so-called median line does not exist,” she said.

- ‘High alert’ -

Monday’s announcement by Taipei came after an uptick in the number of incursions by Chinese warplanes and ships last week.

Beijing said last week its troops were on “high alert” after two ships belonging to the United States and Canada sailed through the Taiwan Strait.

Taiwan’s defence ministry said 68 Chinese aircraft and 10 naval vessels were detected around the island between Wednesday morning and Thursday morning.

Some of those planes and warships were heading to an unspecified area of the Western Pacific to “conduct joint sea and air training” with China’s Shandong aircraft carrier, the ministry said.

The Shandong, one of two operational aircraft carriers in the Chinese fleet, was detected last week around 60 nautical miles (110 kilometres) southeast of Taiwan heading into the Western Pacific, Taipei authorities said.

Japan’s defence ministry also said last week its navy had detected six ships – including frigates, destroyers, one fast combat support ship and the Shandong – sailing through waters some 650 kilometres (400 miles) south of Miyakojima island, east of Taiwan.

It confirmed that jets and helicopters had been detected taking off and landing from the Shandong, though China has not commented officially on any drills being conducted in the Western Pacific.

- ‘Sacred part of China’ -

Analysts said China could be flexing its muscles to counter US influence in the Asia-Pacific, as it leads multiple rounds of military drills with allies across the region.

“China aims to counter the military containment of democratic allies led by the United States,” Su Tzu-yun, an analyst at Taiwan’s Institute for National Defence and Security Research told AFP.

Following last August’s visit to Taipei by Nancy Pelosi, then-speaker of the US House of Representatives, China staged its largest-ever war games around Taiwan.

Then in April this year, Beijing conducted a three-day “Joint Sword” military exercise to simulate the encirclement of the island, after Taiwan’s President Tsai Ing-wen met US House Speaker Kevin McCarthy in California.

In a comment on the Weibo social media platform, China’s Global Times state tabloid said Taiwan was a “sacred and inalienable part of China.”

“The People’s Liberation Army’s relevant combat training activities are necessary actions to safeguard national sovereignty and territorial integrity,” it added, referring to China’s military.