United States President-elect Donald Trump's latest rhetoric questioning the need to adhere to the "one China" policy has prompted the Chinese Foreign Ministry to express its grave concern.
Taiwan, too, is wary of being used as a bargaining chip by Mr Trump to deal with a strong China.
In a swift response to Mr Trump's remarks on Sunday, a Chinese Communist Party-linked newspaper even spelled out the stakes involved if Mr Trump were to abandon the "one China" policy.
The nationalistic Global Times called Mr Trump "as ignorant of diplomacy as a child" in its Chinese-language version, and warned that if the US openly supported Taiwan's independence and ramped up arms sales to the island, China could aid "forces hostile to the US".
Foreign Ministry spokesman Geng Shuang was more restrained as he reminded Washington at a regular press conference yesterday that the healthy development of Sino- US ties and bilateral cooperation in major areas would be "out of the question" if the basis of the "one China" principle is disrupted, or destroyed.
"We urge the new US government and leader to fully recognise the highly sensitive nature of the Taiwan issue," Mr Geng said.
China's response came a day after Mr Trump said in an interview with Fox TV that he did not know why the United States must "be bound by a 'one China' policy unless we make a deal with China having to do with other things, including trade".
Mr Trump complained that "we're hurt very badly by China with devaluation", by China's high tariffs on US goods, and by the militarisation of the South China Sea. He also chided China for not reining in North Korea on its nuclear weapons.
"They're not helping us at all. So, I don't want China dictating to me," he said, referring to the phone call that he took from Taiwan President Tsai Ing-wen on Dec 2.
The phone call marked the first direct contact between the leaders of the two sides since Washington cut diplomatic ties with Taipei in 1979 to re-establish formal relations with Beijing.
And despite reports that the phone call was months in the making, Mr Trump told Fox TV he learnt about the call "an hour or two" before it took place,
The unprecedented move drew widespread concern in the US over whether Mr Trump would discard the country's decades-old policy in dealing with China and what Beijing might do in retaliation.
But so far, China has lodged only a verbal protest with the US.
A commentary by the official Xinhua news agency yesterday reminded Mr Trump to learn from his predecessors on how to conduct Sino- US ties.
The Global Times said Beijing could offer support or military aid to US foes. Beijing "may not prioritise peaceful reunification over a military takeover (of Taiwan) if Trump insisted on his provocations", the newspaper added.
Beijing regards Taiwan as a renegade province, which eventually must be reunited with the mainland.
Taiwanese analysts expressed concern that Mr Trump's tough rhetoric could hurt Taiwan.
Said political analyst Edward Chen I-Hsin: "Taiwan should be worried about being used as Trump's bargaining chip. China will do anything to ensure that its sovereignty over Taiwan is not challenged."