China's security forces detained people Monday at the scene of a rare demonstration as authorities worked to extinguish protests that flared across the country calling for political freedoms and an end to Covid lockdowns.

AFP witnessed police leading two people away from a site in Shanghai where demonstrators gathered over the weekend, while China's censors worked to scrub signs of the social media-driven rallies.

People took to the streets in major cities and gathered at university campuses across China on Sunday to call for an end to lockdowns and greater political freedoms, in a wave of protests not seen since pro-democracy rallies in 1989 were crushed.

A deadly fire last week in Urumqi, the capital of northwest China's Xinjiang region, was the catalyst for the public anger, with many blaming Covid lockdowns for hampering rescue efforts.

But protesters also called for greater political freedoms -- with some even demanding the resignation of China's President Xi Jinping, recently re-appointed to a historic third term as the country's leader.

Large crowds gathered Sunday in the capital Beijing and the economic hub of Shanghai, where police clashed with protesters as they tried to stop groups from converging at Wulumuqi street, named after the Mandarin for Urumqi.

Hundreds of people rallied in the same area with blank sheets of paper and flowers to hold what appeared to be a silent protest on Sunday afternoon.

The BBC said one of its journalists had been arrested and beaten by police while covering the Shanghai protests.

In the capital, at least 400 people gathered on the banks of a river for several hours, with some shouting: "We are all Xinjiang people! Go Chinese people!"

AFP journalists at the tense scene of the Shanghai protests Monday saw a substantial police presence, with blue fences in place along the pavements to stop further gatherings.

Two people were then detained by police at the site, an AFP journalist saw, with law enforcement preventing passersby from taking photos or video of the area.

When asked why one of the people was taken away, a policeman told AFP "because he didn't obey our arrangements" before referring the reporter to local police authorities.

Shanghai police had not responded on Monday to repeated enquiries about how many people had been detained.

An AFP journalist filmed people being detained on Sunday.

State censors appeared to have largely cleaned Chinese social media of any news about the rallies by Monday.

The search terms "Liangma River", "Urumqi Road" -- sites of protests in Beijing and Shanghai -- had been scrubbed of any references to the rallies on the Twitter-like Weibo platform.

- 'Boiling point' - China's strict control of information and continued travel curbs tied to the zero-Covid policy make verifying numbers of protestors across the vast country challenging.

But such widespread rallies are exceptionally rare, with authorities harshly clamping down on any and all opposition to the central government.

Spreading through social media, they have been fuelled by frustration at the central government's zero-Covid policy, which sees authorities impose snap lockdowns, lengthy quarantines and mass testing campaigns over just a handful of cases.

Protests also occurred on Sunday in Wuhan, the central city where Covid-19 first emerged, while there were reports of demonstrations in Guangzhou, Chengdu and Hong Kong.

At the scene of the Beijing riverside rally, where rows of police vehicles were in place on Monday, a female jogger in her twenties told AFP she had seen the protests on social media.

"This protest was a good thing, it sent the signal that people were fed up with too strong restrictions," the jogger, who asked not to be named, said.

"I think the government has understood the message and that they will ease the policy in order to give them and everyone a way out," she added, saying that "censorship couldn't keep up" with news of the protests.

State-run newspaper the People's Daily published a commentary Monday morning warning against "paralysis" and "battle-weariness" in the fight against Covid -- but stopped far short of calling for an end to hardline policy.

"People have now reached a boiling point because there has been no clear direction to path to end the zero-Covid policy," Alfred Wu Muluan, a Chinese politics expert at the National University of Singapore, told AFP.

"The party has underestimated the people's anger."

China reported 40,052 domestic Covid-19 cases Monday, a record high but tiny compared to caseloads in the West at the height of the pandemic.