BUSAN/BEIJING — Chinese leader Xi Jinping and US President Donald Trump held a landmark meeting in South Korea that could reset the volatile relationship between the world’s two largest economies and rival superpowers.

Both leaders offered warm remarks at the start of the talks – their first face-to-face in six years – at an airbase in the coastal city of Busan, near to where an international summit is taking place.

Trump praised Xi as the “great leader of a great country” and said he thought the two “were going to have a fantastic relationship for a long period of time,” while the Chinese leader said it was a “great pleasure” to see Trump after many years.

“We do not always see eye to eye with each other, and it is normal for the two leading economies of the world to have frictions now and then … you and I at the helm of China-US relations should stay the right course,” Xi said, adding the two nations could “prosper together.”

But even against the backdrop of warm handshakes and compliments, Trump also appeared to raise the stakes of the meeting moments before landing in Busan, announcing the end of a more than three-decade moratorium on US nuclear testing.

Trump said the US “has more Nuclear Weapons than any other country,” naming Russia as second and China “a distant third, but will be even within 5 years.”

“Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis. That process will begin immediately,” he wrote.

One hour and forty minutes later the two leaders re-emerged and could be seen shaking hands at the conclusion of their talks. Trump then boarded Air Force One without speaking the the media, ending his consequential tour of Asia.

The world is closely watching for whether the two leaders can stabilize their countries’ fractious relationship during the meeting, which caps off the US president’s five-day, three-country visit to Asia.

The global economy has for months been roiled by a tit-for-tat of mounting tariffs, export controls and other penalties hitting areas from high-tech goods to high-seas shipping, as the US and China have vacillated between escalation and negotiation.

At the crux of those tensions are a gaping trade imbalance and efforts from the US to ensure its national security against an increasingly assertive China, including by expanding restrictions on China’s access to American high tech, like the advanced semiconductors needed to power AI.

On the table before the two leaders, who met at Busan’s Gimhae Air Base, were a range of thorny issues including tariffs, China’s sweeping export controls on rare earths, US restrictions on Chinese access to American high-tech, and China’s role in the illicit fentanyl trade.

China’s purchases of American soybeans, the future in the US of the popular, Chinese-owned social media app TikTok, the war in Ukraine, as well as Taiwan are also topics likely to have been on the leaders’ table over the course of their talks.

A meeting between US and Chinese trade negotiators over the weekend in Kuala Lumpur, Malaysia, ended with both sides appearing optimistic that Trump and Xi could agree to a framework on navigating their ties going forward.

Expectations further rose over the course of the president’s trip to Asia, sources familiar with the matter told CNN, with the hopes that the deal would produce more than just a low-key touchpoint between the two world leaders.

But any agreement reached will be just one touchstone in a thorny and volatile great power rivalry between the world’s superpower democracy and an authoritarian China, whose growing military assertiveness under Xi in the East and South China Seas is rattling US allies in the region.

Both sides have seen a leader-level meeting as key to stabilizing the relationship as they continue to grapple with how to structure their economic ties.

An outcome from Thursday’s talks that does that will be a boon for China, which wants predictability in its US relations while it sprints toward self-sufficiency from American high-tech, and also for Trump, whose meeting with Xi delivers a big-ticket finale for what has already been a dealmaking blitz across Asia.

For all the confidence from trade negotiators in recent days and the leaders’ warm remarks as talks got underway in Busan, whether the meeting would take place at all remained an open question just days ago after a rapid escalation of frictions between the two sides.

Beijing balked at the introduction of a new US rule late last month that vastly expanded the number of Chinese enterprises restricted from accessing certain American technologies, and then, again, when some two weeks later, scheduled US port fees on Chinese-made or Chinese-operated ships went into force.

Chinese officials saw the new rules as a violation of the spirit of their September trade talks in Madrid. Beijing responded not only with its own port fees but the sweeping expansion of export controls on rare earths – a move that rattled Washington.

Trump threatened to respond with an additional 100% tariffs on Chinese imports on November 1 and export controls on software, saying at that time that there was now “no reason” to meet with Xi.

The consequential meeting was meticulously orchestrated by US and Chinese officials.

Trump was originally expected to depart a day earlier, and the White House had planned to meet with Xi in the evening, which could have set up a rushed meeting. Officials ultimately decided to hold the meeting the next day at the airport as Trump departs and Xi arrives for a state visit, the sources said.

Now, with the meeting over but with no readout yet published by either side, observers are watching closely what each was willing to concede to reach an agreement – a delicate balance, as neither of the two strongman leaders would want to be seen by their domestic audiences as conceding too much to a strategical rival. — CNN