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.

Pictures from foreign satellites have shown the barges practicing with civilian Chinese cargo ships and ferries that could carry vehicles and people to be offloaded onto the causeway. China featured the barges on a recent program about military rivalry with Taiwan, warning that they could play a potential role in an attack.

“This equipment is a bridge and a port combined into one,” Wei Dongxu, a CCTV commentator on the show, said of the barges. Once China gains dominance in the skies and seas, he said, ships loaded with military vehicles could dock with the barges and unload the vehicles, enabling heavy combat equipment to land without touching the water. He said of the barges: “Once they appear, that means that the landing has scored a major victory.”

Some American commanders and officials have said that Mr. Xi has ordered the People’s Liberation Army to be able to take Taiwan by 2027. Mr. Xi has not said that China would definitely invade Taiwan, and there is debate about Beijing’s intentions, urgency and capabilities.

Crossing the Taiwan Strait could be perilous for China’s forces, even with more options for getting ashore. The United States could send forces to help Taiwan against China, raising the risk of war between two nuclear powers. Before any attempt by China to land in large numbers — possibly with the barges — the first wave of invading troops could face fierce fighting in the strait and on Taiwan.

But the three landing barges showed that China’s armed forces were rapidly developing ways to get over logistical hurdles of a possible invasion, said J. Michael Dahm, a retired U.S. Navy intelligence officer and co-author of a study of the new barges.

The barges work in sets of three — the longest barge, at 607 feet long, the shortest, 361 feet. The vessels’ legs, when lowered, pin the barges in place and can push the hulls up and above the water, for stability. Each barge also has a tower at the front, which can telescope out a bridge, connecting it to the next barge or to the shore.

The barges form a pier onto which ships that line up alongside the barges could disgorge vehicles. The vehicles could then drive directly along the pier to the shore.

Mr. Dahm said that he used to doubt that the Chinese military would meet Mr. Xi’s goal of readiness by 2027.

“I will tell you my mind has really been changed over just the last 12 to 18 months, seeing the scale of infrastructure and capability improvements that the Chinese have made,” such as the landing barges, he said.

The barges first came to public attention early this year, after H.I. Sutton, a defense analyst, reported that they were being built in a shipyard in Guangzhou.

The Times analyzed satellite imagery and marine traffic data that showed that several commercial ferries and cargo ships took part in the exercises. The commercial ships sidled up to the two larger barges farthest from shore, apparently practicing how to get in place to offload vehicles.

The satellite images did not show any vehicles actually being unloaded. But ferries and cargo ships that took part were of a kind built or modified to handle heavy armed vehicles, like tanks, said Jason Wang, the chief operating officer of ingeniSPACE, a company that analyzes satellite images and other data, including about the Chinese military.

Taiwan’s western coastline, facing the Chinese mainland, has relatively few beaches or ports where landing is easy, and those areas are relatively well guarded. The barges would theoretically enable China to pick other areas on Taiwan’s coast that might be more difficult to land on but are less defended, from which to come ashore, several experts said.

“These barges will open up new locations to deliver troops and material for Xi Jinping to choose from” along Taiwan’s coast, Mr. Wang said. He estimated that in one day the barges could offload hundreds of armored vehicles.

“China still doesn’t have enough gray hull naval ships to assault Taiwan’s main island on their own,” Mr. Wang said, referring to the typical color of warships. But when you add specialized dual-use ferries and cargo ships, “then that becomes a different story,” he said.

“You’re then starting to have enough vessels to be able to deliver a battalion on shore quickly,” he said.

Chinese military planners have closely studied previous wars involving amphibious landings, including Britain’s war to retake the Falkland Islands in 1982, and the D-Day landings at Normandy in 1944.

China may be some way from having a surefire solution to landing on Taiwan. The People’s Liberation Army seems likely to further test the new barges in larger military drills, possibly later this year, said Chieh Chung, a researcher at Taiwan’s Institute for National Defense and Security Research, a government-funded group in Taipei.

“They usually carry out testing through exercises before officially entering into mass production,” he said of China’s military. “Their direction is set — how to overcome all the difficulties that could trouble a joint landing operation.”

During the recent practice runs, it took several hours for the transport ships to dock at the mobile pier, even with help from tugboats. On March 25, one ship appeared to abandon its effort to dock at the pier where two other ships were already berthed. It succeeded the next day and was joined by a small tanker used to refuel the self-propelled barges, making for a total of four ships moored at the same time — a first for the formation.

Mr. Wang, the expert on satellite image analysis, said that at the shipyard in Guangzhou that built the new barges, another set of three was nearly finished and had entered the water for initial tests.

Robin Stein contributed reporting from New York.