President-elect Donald Trump spoke by phone Friday with Tsai Ying-wen, the president of Taiwan. The call was the first in more than 30 years between an American president-elect and a leader of the island.

According to a readout of the call from the Trump transition team, Tsai congratulated Trump on his victory, and the two discussed “the close economic, political, and security ties exists between Taiwan and the United States.”

But the Trump team’s description of the call belies the fact that the conversation has the potential to upset three decades of relations between the United States and its most important global trading partner.

The United States and most of the international community acknowledge China’s claim of sovereignty over Taiwan. But Taiwan, with its own elected government, constitution and military, considers itself an independent nation.

The U.S. cut diplomatic relations with Taiwan in 1979, when it established formal ties with the People’s Republic of China. Trump’s call will likely enrage Beijing, and stands to damage U.S. relations with China before Trump even takes office.

“The Chinese leadership will see this as a highly provocative action, of historic proportions,” Evan Medeiros, a former Asia director at the White House national security council, told the Financial Times, which first reported the call Friday afternoon.

“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,” Medeiros said.

Neither the White House nor State Department were notified of the call beforehand, according to reports.

Trump said on Twitter Friday evening that Tsai initiated the phone call.

The President of Taiwan CALLED ME today to wish me congratulations on winning the Presidency. Thank you! — Donald J. Trump (@realDonaldTrump) December 3, 2016

Interesting how the U.S. sells Taiwan billions of dollars of military equipment but I should not accept a congratulatory call. — Donald J. Trump (@realDonaldTrump) December 3, 2016

But the Taipei Times reported the call was arranged by Trump’s “Taiwan-friendly campaign staff after his aides briefed him on issues regarding Taiwan and the situation in the Taiwan Strait.”

China has reached out to the White House about the call, according to CNN.

The White House said in a statement later Friday that it remained “firmly committed to our ‘one China’ policy,” which holds that Taiwan is part of China.

“Our fundamental interest is in peaceful and stable cross-Strait relations,” White House national security spokesman Ned Price said.

China’s foreign minister said in response to the call that China does “not want any interference or destruction” of the “one China” policy.

“I do not think it will change the one-China policy that the US government has insisted over the years. The one-China principle is the cornerstone of the healthy development of Sino-US relations,” Foreign Minister Wang Yi said in a statement.

The call with Tsai is the latest in a string of conversations between Trump and foreign leaders that have left foreign policy experts and career diplomats shocked and concerned.

Earlier this week, Trump spoke with Pakistani president Nawaz Sharif and said he looked forward to visiting the country as president ― something President Barack Obama has deliberately avoided doing because of the complex, and sometimes duplicitous, security and intelligence relationship between the two countries. Trump also spoke with President Nursultan Nazarbayev of Kazakhstan, a despot and international pariah who has ruled the former Soviet republic since 1989.

On Friday, Trump also spoke to Rodrigo Duterte, the newly elected president of the Philippines. Since taking office, Duterte has encouraged the extra-judicial murder of hundreds of people accused of dealing drugs, and he has suggested that journalists deserve to be assassinated.

In response to the alarm raised by Trump’s phone calls, White House press secretary Josh Earnest on Thursday delicately urged Trump to seek out advice from career diplomats at the State Department. “President Obama benefited enormously from the advice and expertise that’s been shared by those who serve at the State Department,” he told reporters at the daily press briefing.

“I’m confident that as President-elect Trump takes office, those same State Department employees will stand ready to offer him advice as he conducts the business of the United States overseas. Hopefully he’ll take it.”

Democratic Sen. Chris Murphy (Conn.) was more direct with his criticism. “What has happened in the last 48 hours is not a shift. These are major pivots in foreign policy w/out any plan. That’s how wars start,” Murphy tweeted on Friday. “And if they aren’t pivots - just radical temporary deviations - allies will walk if they have no clue what we stand for. Just as bad. It’s probably time we get a Secretary of State nominee on board. Preferably w experience. Like, really really soon.”

This is a breaking story and has been updated throughout.