President-elect Donald Trump called Taiwan's president. Photo / AP
Donald Trump has spoken by telephone with Tsai Ing-wen, the president of Taiwan, risking a major diplomatic row with China.
Beijing firmly views Taiwan as part of a single Chinese nation.
The US and Taiwan have not had formal diplomatic relations since 1979, after the US had implemented a "One China" policy and closed its embassy in Taipei.
It is thought that no US president or president-elect has spoken with a leader of Taiwan since then.
"President-elect Trump spoke with President Tsai Ing-wen of Taiwan, who offered her congratulations," according to a readout of the call released by Trump's transition team.
"During the discussion, they noted the close economic, political, and security ties exists between Taiwan and the United States. President-elect Trump also congratulated President Tsai on becoming President of Taiwan earlier this year."
Mrs Tsai has refused to accept the concept of "One China," prompting Beijing to cut off all official communication with the island's new government.
An official of the Taiwan's representative office in Washington could not confirm the call but said it would be "historic".
"The Chinese leadership will see this as a highly provocative action, of historic proportions," Evan Medeiros, former Asia director at the White House national security council, told the Financial Times.
"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."
Bonnie Glaser, director of the China Power Project at the Center for Strategic and International Studies, said: "I would guess that President-elect Trump does not really comprehend how sensitive Beijing is about this issue."
Earlier this week, Mr Trump risked angering India by apparently telling Nawaz Sharif, the Pakistani prime minister he would "love" to visit the country soon.
He described Pakistanis as "one of the most intelligent people", according to a Pakistani statement on the call.
Trump on Twitter: 'He CALLED ME!'
A statement from Trump's transition team said he spoke with Taiwanese President Tsai Ing-wen, who offered her congratulations.
"During the discussion, they noted the close economic, political, and security ties ... between Taiwan and the United States.
President-elect Trump also congratulated President Tsai on becoming President of Taiwan earlier this year," the statement said.
Trump tweeted later: "The President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you!"
The Taiwanese presidential office issued a statement early Saturday saying Trump and Tsai discussed issues affecting Asia and the future of U.S. relations with Taiwan.
"The (Taiwanese) president is looking forward to strengthening bilateral interactions and contacts as well as setting up closer cooperative relations," the statement said.
"The president also told U.S. President-elect Trump that she hopes the U.S. will continue to support Taiwan's efforts in having more opportunities to participate in and contribute to international affairs in the future," Tsai's office said.
It said the two also "shared ideas and concepts" on "promoting domestic economic development and strengthening national defense" to improve the lives of ordinary people.
The White House learned of the conversation after it had taken place, said a senior Obama administration official, who requested anonymity because of the sensitive diplomatic relations involved.
China's embassy in Washington, its foreign ministry in Beijing and Taiwan Affairs Office did not respond to requests for comment.
Friday's call is the starkest example yet of how Trump has flouted diplomatic conventions since he won the Nov. 8 election. He has apparently undertaken calls with foreign leaders without guidance customarily lent by the State Department, which oversees U.S. diplomacy.
China's response: 'Just a small trick by Taiwan'
Meanwhile, China's foreign minister said today he hopes Beijing's relations with the U.S. would not be "interfered with or damaged" after President-elect Donald Trump broke with decadeslong diplomatic tradition and spoke directly with Taiwan's leader.
Chinese Foreign Minister Wang Yi said the call between Taiwan's president and Trump was "just a small trick by Taiwan" that he believed would not change U.S. policy toward China, according to Hong Kong's Phoenix TV.
"The one-China policy is the cornerstone of the healthy development of China-U.S. relations and we hope this political foundation will not be interfered with or damaged," Wang was quoted as saying.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 U.S. recognizes Beijing as representing China but retains unofficial ties with Taiwan.