By Katie Hunt, Tim Schwarz and Eric Bradner, CNN

December 12, 2016

Beijing (CNN)China has warned that it’s «seriously concerned» after President-elect Donald Trump questioned whether the United States should keep its long-standing position that Taiwan is part of «one China.»

Trump has signaled a willingness to confront Beijing, and his latest comments in an interview with Fox News suggested that he won’t hesitate to anger China until the country comes to the bargaining table on trade and North Korea.

China’s response was measured but clear: co-operation with the US «would be out of the question» if Trump doesn’t adhere to the ‘one China’ policy — a cornerstone of bilateral relations since the establishment of diplomatic ties in the 1970s.

«I want to stress that the Taiwan question has a bearing on China’s sovereignty and territorial integrity,» Chinese Foreign Ministry spokesman Geng Shuang said.

«Adhering to the ‘one China’ principle is the political bedrock for the development US-China relations. If it is comprised or disrupted, the sound and steady growth of the bilateral relationship, as well as bilateral cooperation in major fields would be out of question.»

The language used by the Global Times newspaper, a provocative but state-sanctioned tabloid, went much further in its criticism of Trump.

‘Ignorant child’

In a Monday editorial, it described the President-elect as a «child» ignorant of foreign policy and ruled out negotiations on the «one China» issue.

«The ‘one China’ policy cannot be bought and sold, Trump, it seems, only understands business and believes that everything has a price and that if he is strong enough he can buy and sell by force,» it said.

The editorial warned that Trump, because of his «lack of hands on experience,» was liable to be influenced and controlled by hardliners near him.

It added that if Trump ditched the «one China» policy, it would spark «a real crisis.»

The Communist government in Beijing views Taiwan as a «renegade province,» since Chinese nationalists fled there and established a government after losing the civil war in 1949.

Both governments — officially the People’s Republic of China (PRC) and the Republic of China (ROC) — claim to be the legitimate ruler of all of China, but the ROC effectively controls only Taiwan and a few other small islands.

Controversial call

Trump unleashed a storm of controversy when he took a call from Taiwan’s leader, President Tsai Ing-wen, earlier this month.

Chinese officials were furious over the first conversation in decades between a Taiwanese leader and a US President or President-elect.

Trump’s Taiwan call

Trump then slammed China in a series of tweets, which criticized China’s currency policy and its military posturing in the South China.

On Sunday, the President-elect doubled down: «I fully understand the ‘one China’ policy, but I don’t know why we have to be bound by a ‘one China’ policy unless we make a deal with China having to do with other things, including trade,» Trump said on «Fox News Sunday.»

He suggested that the policy could be a bargaining chip over North Korea — China is the country’s only major ally.

«I mean, look, we’re being hurt very badly by China with devaluation, with taxing us heavy at the borders when we don’t tax them, with building a massive fortress in the middle of the South China Sea, which they shouldn’t be doing, and frankly with not helping us at all with North Korea,» Trump said.

«You have North Korea. You have nuclear weapons, and China could solve that problem, and they’re not helping us at all,» Trump said.

Red line

China watchers are trying to work out if Trump is really ready to challenge the strategic ambiguity of the «one China» policy, which permits Beijing to regard Taiwan as a part of China and the United States to sell the island arms to defend itself.

Some have welcomed the prospect of better ties with Taiwan — a boisterous, multi-party democracy that stands in sharp contrast to China, a one-party state whose rulers are tightening their grip on dissent.

But the diplomatic balance over Taiwan is so delicate that some analysts fear Trump could be starting a confrontation that could easily spin out of control, endanger other crucial areas of the US-China relationship and even risk a military clash in the Pacific.

Michael Auslin, a scholar at the American Enterprise Institute, says it would be foolish to think Beijing will sit by and watch how Trump decides to reform US policy toward Taipei.

«The reality is that Taiwan is the one, non-negotiable red line in US-China relations,» he said.

CNN’s Serenitie Wang in Beijing contributed to this report