President-elect Donald Trump says the US is ready to abandon the policy, unless China agrees to a trade deal.

US President-elect Donald Trump has said the United States does not necessarily have to stick to its long-standing position that Taiwan is part of “one China,” questioning nearly four decades of policy in a move angering Beijing.

Trump’s comments on “Fox News Sunday” came after he prompted a diplomatic protest from China over his decision to accept a telephone call from Taiwan’s president on December 2.

“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 told Fox.

Trump’s call with President Tsai Ing-wen was the first such contact with Taiwan by a US president-elect or president since President Jimmy Carter switched diplomatic recognition from Taiwan to China in 1979, acknowledging Taiwan as part of “one China”.

OPINION: Trump era has Beijing on edge

Beijing considers Taiwan to be a renegade province and the subject is a sensitive one for China.

On Monday, China said that it had “serious concern” about Trump’s comments concerning Taiwan, and warned that any changes to how the US deals with the self-governing island could damage diplomatic ties between Washington and Beijing.

Geng Shuang, a spokesman for China’s foreign ministry, said that established policy is the “political foundation” of any diplomatic relationship between China and the US, and that any damage to it could render cooperation between both sides to be “out of the question.

“We urge the new US leader and government to fully understand the seriousness of the Taiwan issue, and to continue to stick to the ‘one-China’ policy,” Geng said.

Earlier this month, after Trump’s phone conversation with Taiwan’s president, the Obama administration said senior White House aides had spoken with Chinese officials to insist that Washington’s “one China” policy remained intact.

In the Fox interview, Trump criticised China over its currency policies, its activities in the South China Sea and its stance towards North Korea. He said it was not up to Beijing to decide whether he should take a call from Taiwan’s leader.

INFOGRAPHIC: Who’s who in Donald Trump’s administration?

“I don’t want China dictating to me and this was a call put in to me,” Trump said. “It was a very nice call. Short. And why should some other nation be able to say I can’t take a call?

“I think it actually would’ve been very disrespectful, to be honest with you, not taking it,” Trump added.

their country (the U.S. doesn't tax them) or to build a massive military complex in the middle of the South China Sea? I don't think so! — Donald J. Trump (@realDonaldTrump) December 4, 2016

In the Fox interview, Trump brought up a litany of complaints about China that he emphasised during his presidential campaign.

“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.”

Economists, including those at the International Monetary Fund, have widely viewed China’s efforts to prop up the yuan’s value over the past year as evidence that Beijing is no longer keeping its currency artificially low to make Chinese exports cheap.

‘Naive like a child’

The Global Times, an influential tabloid published by the ruling Communist Party’s official People’s Daily, said in an editorial that Trump was “naive like a child on diplomacy” and that the “one China” policy “could not be bought or sold”.

When the time comes, the Chinese mainland will launch a series of “decisive new policies toward Taiwan”, the paper said.

“We will prove that all along the United States has been unable to dominate the Taiwan Strait and Trump’s desire to sell the ‘one China’ policy for commercial interests is a childish urge,” it said.