As tensions mount between Beijing and Washington over an anticipated visit by US House Speaker Nancy Pelosi to Taiwan on Tuesday, several Chinese warplanes fly on sorties over the Taiwan strait.

Chinese Navy warships are deployed and Air Force aircraft carry out sorties near the median line of the Taiwan Strait as yet another warning to Washington over Pelosi's anticipated visit.

Neither side's aircraft usually cross the median line, though China's sorties have been deemed "provocative" by a Reuters source.

CNN on Monday cited a Taiwanese government official and a US official as saying that US House Speaker Nancy Pelosi was expected to visit Taiwan as part of her tour in Asia.

According to the US media outlet, the Taiwanese official said that Pelosi is expected to stay in Taiwan overnight, though it is unclear when exactly will Pelosi land on the island.

The US official said that Pentagon officials "are working around the clock" on monitoring any Chinese movements in the region and securing a plan to keep Pelosi safe, the news outlet added.

Chinese Ambassador to Washington Qin Gang said the Taiwan issue was the most sensitive and important core issue in Sino-US relations.

What is significant about the visit is that it comes at a time of great tensions between the two nations over Taiwan, and it would mark the first visit made by a US House Speaker to the Island since 1997.

She is currently in Kuala Lumpur, Malaysia, on the second leg of her Asia tour. Pelosi landed at a Malaysian air force base ahead of meetings with the prime minister and the speaker of the lower house of parliament, state news agency Bernama reported.

Other stops include South Korea and Japan, but all eyes are drawn to Taiwan.

Chinese National Defense Ministry Spokesperson Tan Kefei warned on July 26 that the Chinese military would not sit back if Pelosi visits Taiwan.

US President Joe Biden said in late July that the US military "thinks it's not a good idea right now, but I don't know what the status of it is."

Nikkei Asia reported on Monday that the US has deployed naval and aerial military assets ahead of Pelosi's trek into Taiwan, as data for naval and aerial tracking shows that military ships and jets are being drawn closer to Taiwan. 

Read more: US military assets deployed ahead Pelosi's potential visit to Taiwan

The news agency added that the assets included the aircraft carrier USS Ronald Reagan, which was previously in Singapore, the amphibious assault ship USS Tripoli and the amphibious assault ship USS America, which were near Japan, as well as over 30 other warships, three submarines, and several fighter aircraft. 

The Wall Street Journal cited a person familiar with Pelosi's visit as saying that some of the US House Speaker meetings have been scheduled for Tuesday evening, but most are set for Wednesday, adding that the meetings are not limited to Taiwanese government officials.

"She’s definitely coming," the person said, indicating that "the only variable is whether she spends the night in Taipei."

Read next: Pelosi has right to visit Taiwan, visit not confirmed - White House

These sorties are not the first in light of Pelosi's anticipated visit, as the Chinese People's Liberation Army on Saturday held military drills with a firing exercise in Fujian, a province in the southeastern region of China, across the strait of Taiwan, according to the maritime administration of Pingtan county. 

If US House of Representatives Speaker Nancy Pelosi visits Taiwan, China's military will "not sit quietly by."

The latest warning was issued during a Chinese Foreign Ministry regular briefing. Spokesperson Zhao Lijian also said that because of Pelosi's status as the "No. 3 official of the US government," a visit to Taiwan, which China claims as its own, would "lead to egregious political impact."