Speaking at a campaign fundraiser in northern California, Biden said Xi had been angered over an incident in February when a Chinese balloon — which Washington says was used for spying — flew over the United States before being shot down by American military jets.

“The reason why Xi Jinping got very upset in terms of when I shot that balloon down with two box cars full of spy equipment is he didn’t know it was there,” Biden said.

“I’m serious. That was the great embarrassment for dictators, when they didn’t know what happened.

“That wasn’t supposed to be going where it was […] and he didn’t know about it,” Biden said of Xi. “When it got shot down he was very embarrassed and he denied it was even there.”

The multi-faceted rivalry between China and the United States turned into a full-blown diplomatic crisis with February’s balloon incident.

Biden, who at 80 is running for re-election, on Tuesday waived off concerns about the Asian giant, telling donors that “China has real economic difficulties”.

The remarks are likely to raise strong objections from Beijing, where US State Secretary Antony Blinken visited just days earlier in an attempt to lower the temperature between the two global powers.

Still on the subject of China and Xi, Biden said, “We’re in a situation now where he wants to have a relationship again.”

Blinken “did a good job” on his Beijing trip, but “it’s going to take time”, Biden added.

The US president did bring up another prickly point regarding communist-ruled China: a recent summit in which leaders of Australia, India, Japan and the United States — known as the Quad group — sought to boost peace and stability in the Indo-Pacific maritime region.

The four countries are “working hand in glove in the South China Sea and the Indian Ocean,” Biden said.

“What he (Xi) was really upset about was that I insisted that we unite the… so-called Quad,” Biden said.

Tuesday was not the first time Biden has made significant, even provocative, statements at fund-raising receptions — usually small-scale events at which cameras and recordings are forbidden but where journalists may listen to and transcribe the president’s opening remarks.

At one such event last October, for example, Biden spoke of the threat of nuclear “Armageddon” from Russia.