US senators have warned China against cracking down on rare widespread protests, saying that any use of force would impact relations with Washington.

In a letter made public Friday, 42 members of the 100-strong Senate recalled the Chinese Communist Party's violent suppression of a student-led democracy uprising centered in Tiananmen Square in 1989.

"We caution the CCP in the strongest possible terms not to once again undertake a violent crackdown on peaceful Chinese protesters who simply want more freedom," said the letter sent Thursday to the Chinese ambassador in Washington, Qin Gang.

"If that happens, we believe there will be grave consequences for the US-China relationship, causing extraordinary damage to it."

The letter was led by Republican Senator Dan Sullivan and Democratic Senator Jeff Merkley. It was signed by senators from both parties but mostly Republicans, including the party's leader in the Senate, Mitch McConnell.

President Joe Biden's administration has been cautious in its public remarks about the protests, emphasizing the right to air grievances peacefully.

State Department spokesman Ned Price said Friday that the people of China should have "the same universal rights that people around the world have" on peaceful assembly.

"We've been clear that people in the PRC have a right, of course, to peacefully protest without fear," Price said, referring to the People's Republic of China.

Secretary of State Antony Blinken earlier called the repression of any demonstrations a "sign of weakness."

China witnessed its most widespread demonstrations since Tiananmen Square starting last weekend sparked by anger over stringent anti-Covid lockdowns, with the protests expanding into calls for more political freedom.

China's vast security apparatus mobilized quickly to smother the rallies although the government also moved to unwind some Covid restrictions.

AFP