President-elect says the US may be willing to change the way it views China and Taiwan unless there are trade concessions
China has warned it is "seriously concerned" about comments made by President-elect Donald Trump which could reverse decades of positive relations between the countries.
Mr Trump has continued to anger officials in China after suggesting he is willing to abandon the One China policy which guides Washington's position on Taiwan.
The President-elect caused outrage in Beijing after he took the call from Tsai Ing-wen, the president of democratically self-ruling Taiwan.
Although the US is Taiwan's main ally and arms supplier, Washington has not had official diplomatic relations with Taipei since 1979, when it switched recognition to Beijing.
Mr Trump is showing no signs of backing down to Beijing, which considers Taiwan a rogue province awaiting unification.
On Sunday, the Republican politician and billionaire businessman said unless the mainland makes concessions on trade and other issues the US may be willing to change the way it views China and Taiwan.
Washington's current One China principle suggests there is "One China" comprising the island of Taiwan and the mainland.
By taking Ing-wen's call Mr Trump appeared to formally dismiss the view held by the Chinese.
Now, Beijing is "seriously concerned" about the future, officials have said.
Foreign ministry spokesman Geng Shuang said if the view on Taiwan is "compromised or disrupted, the sound and steady growth of China-US relations as well as bilateral co-operation in major fields would be out of the question."
Beijing considers Taiwan a "core interest" that affects China's sovereignty and territorial integrity, he said, adding that adherence to the One China policy was the "political bedrock" for relations with the US.
Mr Trump's call with President Tsai Ing-wen was the first such contact with Taiwan by a US president-elect or resident since President Jimmy Carter switched diplomatic recognition from Taiwan to China in 1979, acknowledging Taiwan as part of "one China".
Mr Trump has also criticised Chinese currency policies, its activities in the South China Sea and its stance towards North Korea.