Chinese state media on Monday, (12 December) hit out at Donald Trump after he questioned the four-decade "One China" policy, which recognises Taiwan as part of China, in an interview broadcast on Fox News on Sunday.

An editorial in Global Times, an offshoot of People's Daily, advised Trump "to listen clearly, the One China policy cannot be traded". It went on to say, "China needs to wage resolute struggle against [Trump]," and warned that China "cannot be bullied".

It also slammed Trump for being "as ignorant as a child in terms of foreign policy" and ruled out negotiations over the position. The editorial stated that China would have no reason to "put peace above using force to take back Taiwan" if Trump moved away from the policy.

In the interview to Fox news, Trump defended taking a phone call from Taiwanese President Tsai Ing-Wen and said the US was not necessarily bound to the One China policy. He indicated that the US should use the policy as a bargaining chip rather than as the bedrock of diplomatic ties between the two largest economies of the world.

"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," he said.

For decades China has asked countries that wanted to establish diplomatic relations with it, to sever official ties with Taiwan and recognise there is only one China. In 1979, Jimmy Carter had switched diplomatic recognition from Taiwan to China essentially saying that Taiwan was a part of China.

Trump's contact with the Taiwanese president was the first such by a US president-elect or a president.

Trump went on to say, "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."

Later in the day, the Chinese government said it was "seriously concerned" about Trump's remarks on the policy. Geng Shuang, a spokesperson for China's foreign ministry, said "the sound and steady growth of China-US relations" would be "out of the question" if Trump backed away from the policy.

The policy is the "political bedrock" of relations between the two countries, he added.

Tsai's office declined to comment on the issue.

Beijing had earlier lodged a diplomatic protest with the Obama administration over Trump receiving the phone call from the Taiwan leader.

Editor's note: This article has been amended to incorporate Beijing's response.