Dozens of Chinese internet users have posted desperate pleas for access to their WeChat app accounts after hundreds were banned for posts about a rare street protest in Beijing against President Xi Jinping.

The app is critical to daily life in China, allowing hundreds of millions of people to communicate, make payments, take part in Covid contact tracing and access entertainment, but it is also heavily surveilled by the state.

Hundreds of WeChat users have had their accounts blocked, some permanently, after making reference to a small demonstration in the capital on Thursday that called for Xi's ouster.

It comes at a sensitive time as the ruling Communist Party meets for a five-yearly Congress to anoint Xi to a historic third term in power.

"I have really seriously reflected on my mistake, and I promise... I will definitely strictly abide by the guidelines," wrote one Beijing resident on Friday in a post on another Chinese social network that has since been deleted.

"I sincerely hope your company can unblock my account. In future I will never post an inappropriate video or image again."

Another user who said their WeChat account had been banned permanently said: "I've been extremely anxious since it happened and regret my behaviour."

"I've used this account for 10 years and there are many precious photos and messages from friends on it."

One WeChat user based in the southern city of Guangzhou told AFP their account had some functions temporarily restricted for 24 hours on Sunday after they shared photos in a chat group of posters expressing support for the Beijing protest.

"I can feel the isolation of not being able to like/respond/reply to group chat messages... and I feel even more sympathy for users who have been permanently banned," she said.

Beijing is on high alert for any disruption to the week-long Communist Party meeting which began Sunday, with the city under a blanket of tight security.

Video and photos shared on social media Thursday showed a lone protester draping two hand-painted banners off a bridge with slogans criticising government policies on Covid and calling for the right to vote.

"No Covid tests, I want to make a living. No Cultural Revolution, I want reforms. No lockdowns, I want freedom. No leaders, I want to vote. No lies, I want dignity. I won't be a slave, I'll be a citizen," one banner read.

"Go on strike, remove dictator and national traitor Xi Jinping," read another.

Police and security guards quickly swarmed the bridge and volunteers were deployed to guard other pedestrian bridges across Beijing after the protest, while searches online for the incident were heavily censored.