Donald Trump's use of Taiwan as a bargaining chip has provoked a furious outcry inside China, where it has fanned new flames of nationalism and unleashed calls for China to invade Taiwan.

A week from his inauguration, Mr. Trump said in a Wall Street Journal interview that "everything is under negotiation including 'one China.'" It is the third time he has publicly questioned a principle that most foreign nations, including Canada, have agreed to support – that Taiwan and mainland China form part of a single China.

In response, China this weekend insisted that Beijing treats its claimed ownership of Taiwan as "non-negotiable," saying "there is but one China in the world, and Taiwan is an inalienable part of China."

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But the moderate language of China's official rhetoric is increasingly at odds with its own foreign policy, military and media communities, which have grown more outspoken in demanding a harsh rebuke to the U.S. as Mr. Trump prepares to take office. Some are pushing for China to expand its nuclear arsenal. Others are openly discussing a trade war with the U.S. and military takeover of Taiwan.

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On Monday, state and Communist Party-controlled media lashed out. The China Daily called Taiwan "a Pandora's box of lethal potential," saying if Mr. Trump uses it as a negotiating chip, "a period of fierce, damaging interactions will be unavoidable, as Beijing will have no choice but to take off the gloves."

The Global Times warned that "chaos" will ensue if Mr. Trump tests China, saying Beijing "will be prompted to speed up Taiwan reunification and mercilessly combat those who advocate Taiwan's independence."

Such nationalist fervour comes during a delicate year for Chinese leadership, as groups and individuals inside the Communist Party jockey for influence ahead of the Party Congress this fall, at which a new roster of senior leadership under President Xi Jinping will be finalized. No one in elite Chinese politics wants to provide an opening to rivals by appearing insufficiently tough on the Taiwan issue.

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But some in China's academic establishment are already questioning their country's official response as being too easy on Mr. Trump.

"I would not have expected it to be so soft," said Yan Xuetong, dean of the Institute of Modern International Relations at Tsinghua University.

"The one-China principle is a precondition for China and the U.S. to have formal diplomatic relations," he said. Without that, "according to my understanding, China should stop any formal diplomatic relationship with the U.S."

That would mean recalling ambassadors, a huge step.

But failing to do so, Prof. Yan said, would also be seen as a huge step inside China, since it would suggest Beijing has stepped back from demanding U.S. respect for what is seen as a foundational sovereignty issue.

Better for China to hit back with force, shutting down its embassy in Washington before pursuing more dramatic options, said Shen Dingli, vice-dean of the Institute of International Affairs at Fudan University. He called a trade war "very likely," and military hostilities "increasingly likely."

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"If Mr. Trump is ready to play with fire, let's play," said Prof. Shen, who is among China's top international relations thinkers. "We can prepare to wage a war to unify China." That would involve taking over Taiwan and making it a Chinese province, with a Beijing-appointed governor.

"We have the capability to do it. And Mr. Trump could expedite our process to finish it," Prof. Shen said. Do that, and Mr. Trump would lose Taiwan as a "bargaining chip. We will teach him a lesson, that you are wrong."

Naval expert Li Jie, meanwhile, called for upgrades to China's nuclear arsenal and weapons technology to better counter the Trump administration, an idea published in the nationalist tabloid Global Times.

Such proposals are not official policy. And it is growing more difficult to evaluate the authoritativeness of Chinese academics. China's political atmosphere has grown less open, and universities have been told to exercise greater ideological control over their scholars.

"We don't know if what they tell us is truly a reflection of what they believe or rather what they think they need to say in order to ensure their position and good relations with the Chinese Communist Party," said J. Michael Cole, senior non-resident fellow at the University of Nottingham's China Policy Institute.

The most militaristic drum-beating is unlikely to amount to much, he believes.

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"For now, I sense more bluff than anything," he said, although he worries that in the tension between China, Taiwan and the U.S., miscommunication could spark accidental conflict.

"Nerves are on edge in Beijing; I'm not sure how much longer the calmer heads there will be able to hold the zealots in check," he said.

So far, China is holding the line on calm. On Monday, foreign ministry spokesperson Hua Chunying reiterated China's position on Taiwan, saying "anyone who tries to take this one China policy as a bargaining chip, for whatever motive, will be met with firm opposition."

Mr. Trump is not yet in the White House, and hope remains in Beijing that some sort of bargain can be struck to persuade him to change course. The president-elect is still seen as a deal maker, and China is willing to negotiate on trade and investment issues, scholars said. How Mr. Trump's administration will act is also not clear, given that his nominee for secretary of state, Rex Tillerson, said last week, "I don't know of any plans to alter the 'one-China' position."

If Mr. Trump deviates from that, Beijing could refuse to recognize the credentials of his chosen ambassador to China, Terry Branstad. "That would be the first signal to the U.S. that, no, we're not going to have business as usual if you are not following the one-China policy," said Bonnie Glaser, director of the China Power Project at the Center for Strategic and International Studies.

Beijing also has many levers to squeeze Taiwan economically, a response that doesn't risk direct conflict with the U.S.

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"They are very far from a decision that says we are now abandoning peaceful reunification and have to use force," Ms. Glaser said.

Inside China, however, such niceties have faded in favour of heated conversation. If Mr. Trump "wants to use Taiwan as a chip to bargain with China, China will ask him whether he really is ready to go to war over Taiwan," Cao Jingxing, a well-known commentator for Hong Kong broadcaster Phoenix TV wrote Sunday evening on Chinese social media.

It's all part of a "debate happening within China on how we could hit [Mr. Trump] back," said Zhu Feng, executive director of the China Center for Collaborative Studies of the South China Sea at Nanjing University.

It may not always be rational – Prof. Zhu discounts as far-fetched the notion that China is prepared to use military means to overtake Taiwan.

That doesn't mean it should be entirely discounted.

"I hope China's media debate could be some sort of warning to Washington thinkers and policy makers that it's useless to test China's bottom line," he said.