- Video report by ITV News China Correspondent Debi Edward
Donald Trump has spoken to the president of Taiwan, breaking with decades of US policy and potentially causing a diplomatic rift with China.
The call, which was first reported in the Taipei Times, is believed to be the first between a US president or president-elect and a leader of the Asian island since ties were formally severed in 1979.
China sees Taiwan as a breakaway province and has previously threatened to take it by force.
Mr Trump's transition team said President Tsai Ing-wen congratulation him on his election victory, and that both leaders spoke of "close economic, political and security ties" between the US and Taiwan.
The US closed its embassy in Taiwan in the late 1970s following the landmark rapprochement between Beijing and Washington, which emanated from Richard Nixon's 1972 trip to China.
Washington has since officially viewed Taiwan - an independently governed island - as part of the same nation as the Chinese mainland.
Mr Trump's spokeswoman Kellyanne Conway said the president-elect is "well aware" of the US policy on Taiwan.
"President-elect Trump is fully briefed and fully knowledgeable about these issues on an ongoing basis, regardless [of] who is on the other end of the phone," Ms Conway told CNN.
Mr Trump later posted the following tweets:
China's Minister of Foreign Affairs Wang Yi said in a statement published in the People's Daily, China: "China firmly opposes any official interaction or military cooperation between the US and Taiwan."
Mr Yi also dismissed Mr Trump's phone call with the Taiwan premier as a "petty action", Hong Kong-based Phoenix Television reported.
He added that he hopes Beijing's relationship will not be "interfered with or damaged" and dismissed the call as "just a small trick by Taiwan".
"The one-China policy is the cornerstone of the healthy development of China-US relations and we hope this political foundation will not be interfered with or damaged," Mr Wang said.
The White House said in a statement that there was "no change" to its "longstanding policy on cross-strait issues and one China policy" after Mr Trump's phone call.
Washington has pursued a so-called "one China" policy since 1979, when it shifted diplomatic recognition of China from the government in Taiwan to the communist government on the mainland.
Under that policy, the US recognises Beijing as representing China, but retains unofficial ties with Taiwan.
Political analysts predicted that the unexpected call could infuriate Beijing, which issued a bitter protest when the US sold weapons to Taiwan under an established arms agreement.
Evan Medeiros, Asia director at the White House national security council, told the Financial Times: "The Chinese leadership will see this as a highly provocative action, of historic proportions.
"Regardless if it was deliberate or accidental, this phone call will fundamentally change China’s perceptions of Trump’s strategic intentions for the negative.
"With this kind of move, Trump is setting a foundation of enduring mistrust and strategic competition for US-China relations."