Three Chinese ships, including the Shandong aircraft carrier, sailed through the Taiwan Strait on Saturday, which an expert said was an "unusual" display of Beijing's military might during a prolonged period of tensions.
China claims self-ruled democratic Taiwan as its territory, and has vowed to take it one day -- by force if necessary.
Since Taiwanese President Tsai Ing-wen -- who rejects that the island is part of China -- was elected in 2016, Beijing has ramped up air and sea incursions around the island.
The presence of Chinese warships is constantly monitored and announced near-daily by Taipei, but an aircraft carrier passing through the 180-kilometre-wide (112-mile-wide) Taiwan Strait has not been seen since March 2022.
"A (People's Liberation Army Navy) flotilla of 3 ships, led by the Shangdong aircraft carrier, passed through the Taiwan Strait around noon today," Taiwan's Ministry of National Defense said in a statement, referring to China's navy.
The flotilla went "to the west of the median line, heading northward", it added, referring to the unofficial border in the middle of the strait which separates the island from continental Asia.
Saturday's latest show of force from Beijing comes more than a month after China launched aerial and naval exercises around the island.
During the April war games, Beijing simulated targeted strikes on Taiwan and encirclement of the island, including "sealing" it off, and state media reported dozens of planes had practiced an "aerial blockade".
The Shandong also participated in those exercises, with J15 fighter jets deployed from it -- though the vessel was not in the Strait, but southeast of Taiwan.
The war games were a response to Tsai's meeting with US House Speaker Kevin McCarthy in early April, an encounter Beijing had warned would provoke strong countermeasures.
Taiwan's armed forces said Saturday they have deployed air patrol aircraft, navy vessels and land-based missile systems in response to the sail-through.
"We are closely monitoring their movements and will respond accordingly," the defence ministry said on Twitter.
In recent days, the island has seen an increased presence of Chinese ships and warplane incursions.
The ministry said 33 warplanes and 10 vessels were detected in the 24 hours to 6:00 am Saturday.
The day before, 11 vessels were near Taiwan's waters.
Steve Tsang, the director of London-based SOAS China Institute, said sailing the Shandong aircraft carrier through the Taiwan Strait was "very unusual".
"But the Chinese have been trying to display their military might around Taiwan in the past six months to a year, so in that context it is fitting into a general pattern," he told AFP.
Tsang said it also displayed a "lack of understanding" of modern military warfare.
"In the modern era of powerful anti-ship missiles, why would you send a very big ship into a relatively narrow strip of water with limited manoeuvrability?" he said, adding that the sail-by was "a message".
China has not issued a statement on the passage through the Strait.
The last time officials confirmed the Shandong sailed through the Taiwan Strait was in March 2022, right before China's Xi Jinping and US President Joe Biden held a phone call.
Before that, the carrier transited in December 2020, a day after a US warship had passed through. The Shandong also made a sail-by in December 2019, weeks before Taiwanese voters went to the polls.