House Speaker Nancy Pelosi arrived in Taiwan on Tuesday, defying Beijing’s stern warnings against a visit that the Communist Party of China regards as a challenge to its sovereignty.

Mrs. Pelosi, the highest-ranking US official to visit the island, which Beijing claims as part of its territory, is scheduled to meet with Taiwan President Tsai Ing-wen and legislators on Wednesday.

The plane carrying Mrs. Pelosi and other Democratic lawmakers took a circuitous route out of Malaysia’s capital of Kuala Lumpur on Tuesday afternoon, appearing to avoid transiting the South China Sea, where Beijing has an established military presence. At 10:44 p.m. local time, the plane touched down in Taipei.

The Chinese military retaliated with a show of force. According to Chinese state broadcaster China Central Television, the People’s Liberation Army sent an unspecified number of Russian-made Su-35 fighter jets “flying across the Taiwan Strait.”

The closely watched Asia tour has heightened tensions between China and the United States, with Chinese diplomats and the People’s Liberation Army repeatedly threatening retaliation if Mrs. Pelosi goes ahead with the visit. If Washington mishandles the situation between China and Taiwan, China’s Foreign Ministry has warned of potentially “disastrous consequences.”

China is conducting additional military exercises off its coast this week, in addition to those that began over the weekend. Live shelling was planned in the Bohai Sea off China’s northeastern coast from Monday to Thursday, according to notices posted by Chinese maritime-safety authorities. From Tuesday to Saturday, another set of exercises was scheduled in waters just east of the southern island province of Hainan.

As a deterrent, the Pentagon has increased the number of naval forces operating in the region. According to defense officials, the aircraft carrier USS Ronald Reagan, which was ordered last week to leave a port call in Singapore, was in the Philippine Sea with its accompanying ships and the amphibious assault ship USS Tripoli.

The PLA’s Eastern Theater Command, which oversees military forces closest to Taiwan, released a 212-minute video on social media Monday evening showing Chinese air, sea, and land forces training and firing missiles.

According to US officials, Beijing appeared to be preparing to respond to the visit by staging military drills, firing missiles into the Taiwan Strait or near the island, or dispatching more aircraft and naval vessels into areas closer to Taiwan where they had not previously operated.

In an analysis released on Tuesday, political-risk advisory firm Eurasia Group predicted that China’s response would be “unprecedented but not unhinged.”

The Shanghai Composite Index fell 2.3 percent as investors weighed the risk of increased tensions between Beijing and Washington and speculation mounted over Mrs. Pelosi’s visit, which has not been officially sanctioned by President Biden’s administration. Some defense-related companies’ stock prices have risen.

On Monday night, China’s UN representative compared Mrs. Pelosi’s visit to that of then-House Speaker Newt Gingrich in 1997, saying that Chinese leaders at the time made a mistake by tolerating it.

Beijing initially opposed Mr. Gingrich’s plan and threatened retaliation. Mr. Gingrich, on the other hand, began his trip to Taiwan with a high-profile visit to Beijing, where he met with Chinese leaders.

Aside from a political and economic response, Beijing could order military exercises within Taiwan’s air-defense identification zone and across the Taiwan Strait median line, which serves as a de facto boundary, and China’s air force could shadow Mrs. Pelosi’s plane as it approaches Taiwan, according to Eurasia Group.

Mrs. Pelosi’s whereabouts were being tracked and discussed on social media platforms in China and around the world. On Tuesday afternoon, many users of the flight-tracking website Flightradar24 tracked the movement of a US military plane that was thought to have brought Mrs. Pelosi and her delegation to Singapore and then to Malaysia to meet Prime Minister Ismail Sabri Yaakob and other senior officials.

As that plane took off from Kuala Lumpur at 3:42 p.m., as many as 300,000 users tracked its path, speculating that the speaker was on board and wondering if it would head north toward Taiwan.

Some went offline after the tracker showed the plane flying east toward an unknown destination. However, by 9:30 p.m., it had turned north and appeared to be approaching Taiwan, with the Taipei Songshan Airport listed as its next stop on the tracking website.