In recent weeks, China has been practicing unusual maneuvers off its southern coast involving three special barges. The vessels have linked up one behind another, forming a long bridge that extends from deeper waters onto the beach.

That feat has been a warning to Taiwan.

The vessels’ debut suggests that China’s People’s Liberation Army may be a step closer to being able to land tens of thousands of troops and their weapons and vehicles on Taiwan’s shores, experts say. Developing that capability has been a priority of China’s leader, Xi Jinping, in his quest to absorb Taiwan — either by negotiations or by war.

China has been conducting military exercises around Taiwan for years, including a new surge this week. But even as China’s drills have intensified, and its missiles, warships and fighter jets have advanced, many experts have doubted that the Chinese military could cross the Taiwan Strait with the speed and numbers needed for a successful invasion. Strong winds and currents for much of the year add to the dangers of trying to land on Taiwan.

If the new barges go into service, they could expand China’s options for where and when to land on Taiwan, making Mr. Xi’s threat of a possible invasion more plausible.

The vessels have been practicing in waters about 220 miles southwest of Guangzhou, the city where they were built. The barges have retractable, heavy-duty legs that work like giant stilts. The legs protrude from the deck when in transit and are lowered, when the vessels are in position, onto the seabed to steady the vessels against the waves. The barges then thrust out long extendable bridges, forming a 2,700-foot causeway that links the vessels together and connects to the shore.