Taiwan’s coastguard said it warded off 16 mainland Chinese vessels in one day after they sailed into the island’s self-defined restricted waters in a coordinated, multi-pronged operation that experts say points to a shift in Beijing’s maritime pressure tactics.

The vessels – 12 coastguard and research ships, as well as four fishing boats – operated simultaneously on Sunday in waters east of Hualien, south of Pingtung, southwest of Kaohsiung and around the Taiwan-controlled Dongsha Islands, according to the Coast Guard Administration (CGA).

“The CGA monitored the maritime situation throughout the operation and immediately dispatched coastguard vessels to forward positions, where they closely monitored the mainland vessels and broadcast warnings ordering them to leave,” it said in a statement on Sunday.

The agency described the activities as “hybrid warfare” intended to expand Beijing’s jurisdictional claims.

It accused Beijing of pursuing “law enforcement in name, expansion of authority in reality” to create the impression that it exercised jurisdiction over the waters.

The operation comes amid growing concern among security experts that Beijing is increasingly using coastguard, maritime law enforcement and research vessels to apply pressure around Taiwan, rather than relying predominantly on the People’s Liberation Army.

Ma Chen-kun, a professor of PLA affairs at National Defence University in Taoyuan, said Beijing’s focus had gradually shifted this year from navy-led grey-zone operations towards asserting jurisdiction through coastguard, maritime patrol and research vessels.

“For Beijing, such measures produce more concrete results than conventional military grey-zone operations,” Ma said.

He described the approach as a strategy of “leaving the islands but taking away the surrounding seas” – gradually squeezing the waters around Taiwan and its outlying islands without provoking an outright military conflict.

Ma said the approach, already evident in the South China Sea, was increasingly being seen in waters east of Taiwan as well as around Quemoy, Matsu, Dongsha and the Taiwan-controlled Taiping Island in the South China Sea’s Spratly archipelago. Quemoy is also known as Kinmen.

His assessment broadly echoes an October 8 analysis by the International Institute for Strategic Studies, which said Beijing had stepped up law enforcement, maritime surveillance, fisheries and research activities east of Taiwan since June.

The London-based think tank described the proliferation of mainland Chinese actors as a significant development in Beijing’s grey-zone strategy, potentially aimed at establishing a more complex system of maritime governance around Taiwan involving military and civilian agencies.

The increased activity has also raised questions over whether Taiwan can sustainably respond vessel-for-vessel without straining its own coastguard resources.

Dennis Blair, a retired US Navy four-star admiral and former commander of the US Pacific Command, said in a video address to a maritime security conference in Taipei last week that Taiwan should not automatically shadow every mainland ship or aircraft.

Taipei should instead allocate its limited resources according to the level of threat, retain operational flexibility and strengthen maritime surveillance, law enforcement and self-defence capabilities, he said.

Taipei has increasingly looked to learn from the Philippines and its policy of “active transparency”, under which Manila has publicised confrontations with mainland Chinese vessels in the South China Sea.

Taiwan’s coastguard plans to send a vessel carrying about 100 officers and students to the Philippines next October, its first such visit in 53 years. Taipei also donated a retired patrol vessel to Manila last month.

Taiwan’s National Security Council deputy secretary general Lii Wen has called for greater technological and maritime law enforcement cooperation between the two in areas including maritime domain awareness, unmanned systems and less-lethal weapons.

Sunday’s operation was the latest in a series of encounters this month. Taiwan’s coastguard said it had driven mainland coastguard vessels away from waters around Dongsha on 11 occasions this year, involving 14 vessel appearances before the latest operation.

Since the start of this month, it has warded off 29 mainland coastguard, research, survey and fishing vessel appearances, including 16 from Sunday.

In a more serious incident on October 1, a Taiwanese coastguard vessel used a water cannon to drive away a mainland fishing boat that refused to leave restricted waters near the Dongsha Islands, prompting a strong protest from Beijing.

For Ma, the broader significance lies in Beijing’s apparent effort to turn repeated peacetime activity into assertions of jurisdiction – pressure that remains below the threshold of armed conflict but could gradually reshape practices in waters surrounding Taiwan.

Blair warned that the threshold would change sharply if Beijing escalated pressure by intercepting or boarding commercial vessels, forcing them to change course or imposing an effective blockade.

Such actions, he said, would move beyond grey-zone coercion and amount to acts of war.

Beijing regards Taiwan as part of China to be reunited by force if necessary. Most countries, including the US, do not recognise Taiwan as an independent state, but Washington is opposed to any attempt to take the self-ruled island by force and is committed to supplying it with weapons.