TAIPEI - Taiwan's Ministry of Foreign Affairs has confirmed that a plane carrying US House Speaker Nancy Pelosi from Kuala Lumpur to Taipei is scheduled to land at 10.30pm local time on Tuesday (Aug 2).

The trip would make her the highest-ranking US politician to visit the island in 25 years.

Her SPAR19 flight first flew southeast towards Borneo before circling up north towards the direction of the Philippines and Taiwan, according to flight-tracking website Flightradar24.

The roundabout path appeared to have avoided the South China Sea where China's People’s Liberation Army (PLA) has held various exercises, including live fire drills, since last week.

Beijing, which regards Taiwan as a renegade province that will be retaken by force if necessary, views such a visit as sending an encouraging signal to the pro-independence camp on the self-ruling island. It has issued increasingly severe warnings over Mrs Pelosi's potential visit and has not ruled out a military response.

China earlier on Tuesday said it was in communication with the US over the expected visit, warning that Washington will "pay the price" as it extended air traffic controls around Xiamen, the coastal city closest to the island.

China's foreign minister Wang Yi said those US politicians who "play with fire" on the Taiwan issue will "come to no good end", according to a ministry statement. 

He did not specify any US politician.

Similar comments were made earlier on Tuesday by China's foreign ministry spokesman, Ms Hua Chunying.

"What I can tell you is, the US will definitely have to bear responsibility and pay the price for harming China's sovereignty and security interests," Ms Hua told a regular press briefing in Beijing, adding that China will take "firm and powerful" measures in response.

"If the US misjudges or handles the situation across the Taiwan Strait incorrectly, it will have catastrophic consequences for the security, prosperity and order of the Taiwan region and the world at large."

Mrs Pelosi has been on a tour of the Indo-Pacific which started in Singapore on Monday, followed by Malaysia, though Taiwan does not feature on the official agenda.

Citing an unnamed source, Reuters reported that Chinese planes and warships on Tuesday morning came close to the median line in the Taiwan Strait between China and Taiwan, with Chinese aircraft briefly "touching" the median line in a "very provocative" act. The US Navy has also reportedly deployed four warships in waters east of Taiwan in what it called “routine” deployments.

Meanwhile, Xiamen Air said in an announcement on its website that some 30 flights have been affected by "(traffic) flow control", without providing further details.

Most of the flights were heading from other Chinese cities to Xiamen, Fuzhou and Quanzhou in Fujian province. According to Flightradar24, the affected flights had paths crossing over the South China Sea, and have since been rerouted to take inland routes instead.

The Maritime Safety Administration also announced live firing exercises in parts of the Bohai Sea and South China Sea, barring vessels from entering both areas till midnight Saturday.

"Based on what I know, in response to Pelosi's possible visit to Taiwan, Beijing has formulated a series of countermeasures, including military actions," wrote nationalist commentator Hu Xijin on Twitter.

The retired editor-in-chief of the nationalist Global Times tabloid deleted a tweet over the weekend warning of military retaliation after Twitter blocked his account.

But the view that China should take military action is a popular one on Chinese social media, where eight of the top 10 trending topics on the Weibo microblogging platform were linked to Mrs Pelosi's visit. Many netizens include references to the might of the PLA, which just marked its 95th anniversary on Monday.

The Chinese hashtag, "the Chinese military dares to draw its sword", drew over 100 million engagements, while the top hashtag, "Twitter users mock Blinken's comments on Pelosi's Taiwan visit" drew 330 million engagements.

US Secretary of State Antony Blinken said on Monday that a potential visit to Taiwan by Mrs Pelosi would be entirely her decision, but called on China not to escalate tensions in the event of a visit.

Many comments online appeared to be gleefully anticipating a military response.

"This is the sound of (China) welcoming the witch," read the top comment on a video of military exercises posted by the Eastern Theatre Command of the PLA,which drew nearly 8 million views.

The unit had said on Monday that it was ready and awaiting battle orders.

"(China's) response will most certainly include a military component, most likely with a show of force in the first instance," tweeted Dr M. Taylor Fravel, an expert on the PLA at the Massachusetts Institute of Technology.

The response is likely to include economic and diplomatic actions targeting Taiwan, he added, and is likely to unfold in the days and weeks after Mrs Pelosi leaves Taiwan.

"The goal will be to underscore resolve without sparking escalation, but the likely prominence to the military component will include the potential for miscalculation," he said. "There are also significant US naval assets in the region at the moment."

Beijing on Monday banned shipments from over 100 Taiwanese food exporters in an apparent effort to impose economic sanctions on the island, claiming that information on import documents were outdated.

Affected products include seafood, tea and honey.

China had previously banned pineapples and certain types of apples from Taiwan, and then expanded the ban to Taiwanese grouper in June, citing prohibited chemicals found on the fish.

Meanwhile, China's representative to the UN called Mrs Pelosi's visit "dangerous and provocative".

"(The visit) will send a seriously wrong signal to the separatist elements seeking 'Taiwan Independence', undermine the one-China principle, undermine China's sovereignty and territorial integrity, undermine the peace and stability in the Taiwan Strait, and undermine the relationship between China and the US," Ambassador Zhang Jun told journalists at a briefing in New York.

China is fully prepared to respond and if the visit continues, the US will have to bear "all the serious consequences arising thereof".

Referring to a similar visit to Taiwan by then Speaker Newt Gingrich in 1997, Mr Zhang called it a "previous mistake" that does not legitimise future missteps.

While US lawmakers frequently make such visits to Taiwan, Mrs Pelosi - being second in line to the American presidency - would be the most senior politician to visit in two-and-a-half decades.

During his call with US President Joe Biden last week, President Xi Jinping had also voiced his objection, calling on Washington to abide by the "one-China policy", adding that "those who play with fire shall perish by it".

While Washington does not have official diplomatic ties with Taipei, it is obligated by US law to provide it with the means to defend itself.

While the Biden administration is understood to be opposed to Mrs Pelosi's Taiwan stop, White House National Security Council spokesman John Kirby said she was entitled to go where she pleased.

"The Speaker has the right to visit Taiwan," he told reporters. "There is no reason for Beijing to turn a potential visit consistent with longstanding US policies into some sort of crisis."