A day earlier, the former commander of the U.S. Army in Europe predicteda conflict between the global powers.
"I think in 15 years, it's not inevitable, but it is a very strong likelihood that we will be at war with China," retired Lt. Gen. Ben Hodges told the Warsaw Security Forum.
His comments echoed former White House chief strategist Steve Bannon, who said in 2016: "We're going to war in the South China Sea in five to 10 years, there's no doubt about that."
Bannon specifically pointed to a network of military bases Beijing has built on artificially enlarged coral reefs in the hotly contested body of water. These militarized outposts feature runways, sea ports, and multi-story buildings, and there have even been reports of missile deployments.
Many experts agree that this type of tough talk carries grave risks. But most believe the world is a considerable ways away from a war between its two largest economies.
"There's clearly been a sharpening of the rhetoric between the two countries, and we're currently seeing a real push in worrying direction," says Raffaello Pantucci, director of International Security Studies at the Royal United Services Institute, a think tank based in London. "There's a genuine concern it might end up somewhere horrible."
Xi didn't mention any enemy by name when he made the comments, but they came during a tour at the Southern Theatre Command, in Guangdong province, which is responsible for monitoring Taiwan and the South China Sea.
China claims a huge chunk of this sea as its own, giving it control over a crucial, oil-rich choke-point through which $5.3 trillion of trade passes each year.
It was here in September that a Chinese warship came within 45 feet of colliding with the USS Decatur. This near miss was during one of the fairly regular voyages by U.S. ships and planes into these waters, an attempt by Washington to show Beijing it can't restrict freedom of passage.
Experts predict it won't be the last time. The U.S. and China "will meet each other more and more on the high seas," Admiral John Richardson, chief of U.S. Naval Operations, said at an event in Jakarta on Tuesday.
Hodges said that September's maritime near-miss was only one example of "an increasingly tense relationship" between the countries.
Other points of friction, Hodges said, are China's vast infrastructure projects in Asia, Europe and Africa, as well as its "constant stealing of technology."
Then there's Taiwan. China considers the island a runaway province, the U.S. has sold it $25 billion of arms since 2007. Last month, when the Trump administration approved the sale of $330 million of F-16 parts, Beijing said it lodged "stern representations" against the move.
While it's not in U.S. or Chinese interests to start a war, one way this might happen is through a misunderstanding or bad communication, especially if animosity over the trade war means the sides stop speaking with each other.
"The Chinese might think, 'We're going to build a base here,' and the Americans decide, 'That one is too far,'" according to Pantucci. "Or two boats bump into each other, or something happens with Taiwan."
While such scenarios are worrying, Pantucci said they're not quite the precursor to the all-out combat imagined by more hawkish types.
"Are we going to see a conflict soon, like Steve Bannon's doomsday proclamation? I tend to be a little less apocalyptic than that. I tend to think that cooler heads will eventually prevail," Pantucci added.
One thing to remember in this discussion, according to experts, is that China is not Russia.
Russia has a relatively small economy and is less powerful than it was 30 years ago. It punches above its weight by sewing chaos, and using hard power in places such as Syria, Ukraine and Georgia, not to mention the ever-present threat of nuclear annihilation.
"That is not China's game; China's game is to become the world's biggest power," Pantucci says. "It doesn't want a nuclear war, because nuclear war is not conducive to growth."
Those seeking reassurance can also look to the trade war that is starting to bite on both sides of the Pacific.
Share markets soared Friday after a phone call between Trump and Xi resulted in a positive tweet from the American president.
Nevertheless, the damage is starting to show. Some 85 percent of U.S. companies and 70 percent of Chinese companies surveyed said they have suffered from the tariffs, Reuters reported, citing a poll by the American Chamber of Commerce in South China.
This mutual pain would be even greater were a military conflict to break out, according to Gregory B. Poling, director of the Asia Maritime Transparency Initiative at the Center for International and Strategic Studies
The U.S. and China "have a couple things going for them that no other two great powers ever have," he says.
"They are economically intertwined in a way that raises the costs of conflict for both," he adds, "and they are operating in an international web of institutions and norms that are help blunt their worst impulses and offer avenues for peaceful contestation."
Most Americans don't seem too bothered. An October poll by the Chicago Council on Global Affairs found less than four in ten people said that the development of China is a critical threat to U.S. interests.
Poling recognizes that the South China Sea and Taiwan are "potential triggers" for a conflict, but for now, will he be losing sleep over it?
"Not tonight, no," he says.