Moment Antony Blinken winces and shakes his head when Biden calls Xi a 'dictator' at San Francisco press conference after four-hour high-stakes talks

Antony Blinken, America's top diplomat appeared to shake his head in irritation as Joe Biden went off script and called Xi Jinping a 'dictator' at the end of a carefully choreographed summit.

The four-hour meeting between Biden and Xi on Wednesday followed months of diplomatic efforts to lay the groundwork, including a trip by Blinken to Beijing.

It was the first time for over a year that the leaders of the world's two largest economies had met in person.

Both sides initially called the talks a constructive breakthrough that had reduced tensions on a host of issues.

However, at a subsequent news conference, Biden said he regarded Xi as a 'dictator,' adding 'Look, he is.'

That drew a furious response from Beijing which called Biden's remarks 'irresponsible'.

As Biden made the undiplomatic comments Blinken, sitting in the front row a few feet from the president on the stage, appeared to flinch.

He jerked his head to the side and clasped his hands more tightly.

Biden was holding the news conference alone without Xi at the secluded Filoli estate outside San Francisco.

The president had previously referred to Xi as a dictator in June, and was asked if he still holds that view.

He responded: "Look, he is. He's a dictator in the sense that he's a guy who runs a country that is a communist country that's based on a form of government totally different than ours.'

China's foreign ministry quickly said it "strongly opposes" the view expressed by Biden.

"This statement is extremely wrong and irresponsible political manipulation," foreign ministry spokesperson Mao Ning said.

"It should be pointed out that there will always be some people with ulterior motives who attempt to incite and damage U.S.-China relations, they are doomed to fail."

Last March Xi clinched a third term as president when nearly 3,000 members of China's rubber-stamp parliament, the National People's Congress, voted unanimously for him in an election in which there was no other candidate.

Xi is considered the most powerful Chinese leader since Mao Zedong, after a decade of consolidating power in policy-making and the military, and stifling media freedoms.

There was no immediate reaction from the Chinese delegation in the U.S., which had come to the United States to attend the Asia-Pacific Economic Cooperation summit.

Hundreds of critics of Beijing marched through downtown San Francisco on Wednesday chanting "Free Tibet" and "Free Hong Kong."

When Biden made a similar dictator reference in June, China called the remarks absurd and a provocation.