Protests against Covid restrictions which erupted over the weekend appear to have died down, as a heavy police presence is reported in Chinese cities.
Large barriers have gone up along the main protest road in Shanghai and police have made several arrests.
They have been stopping people taking photos of the protests and deleting pictures on their devices.
Nationwide protests grew after a fire in a high-rise block in Urumqi, western China, killed 10 people on Thursday.
It is widely believed residents could not escape the blaze because of Covid restrictions, but local authorities have disputed this.
A BBC journalist was detained while covering a protest in Shanghai on Sunday. Ed Lawrence was beaten and kicked by the police during his arrest, and held for several hours before being released.
UK Foreign Secretary James Cleverly tweeted that the arrest was "deeply disturbing".
China remains the only major economy with a strict zero-Covid policy, with local authorities clamping down on even small outbreaks with mass testing, quarantines and snap lockdowns.
Many images of anti-lockdown protests have emerged from Shanghai and the capital Beijing, as well as other major urban areas like Chengdu and Wuhan.
Censorship has gone into overdrive on Chinese social media platforms since the weekend's protests, to stop people seeing and discussing them.
Tens of millions of posts have been filtered from search results, while media are muting their coverage of Covid in favour of upbeat stories about the World Cup and China's space achievements.
Dozens of protesters gathered in central Hong Kong on Monday, and at the campus of the Chinese University of Hong Kong, in a show of solidarity with demonstrations across China.
China's vaccine problem
While China developed its own Covid vaccines, they are not as good as the mRNA technology - such as the Pfizer and Moderna shots - used elsewhere.
Two doses of the Pfizer/BioNTech vaccine gives 90% protection against severe disease or death vs 70% with China's Sinovac.
BBC journalist detained during China protests
Covid protests grip China's major cities
Blank paper becomes the symbol of China's protests
The vaccines have also not been given to enough people. Far too few of the elderly - who are most likely to die from Covid - have been immunised.
There is also very little "natural immunity" from people surviving infections as a consequence of stopping the virus in its tracks.
It means new variants spread far more quickly than the virus that emerged three years ago and there is a constant risk of it being imported from countries that are letting the virus spread.
The Chinese government has not acknowledged the protests or responded in any formal way.
They pose an unprecedented political challenge for Chinese President Xi Jinping, with the country watching as to how he will respond.
Large numbers of protesters have been holding up blank sheets of paper - a tactic to protest while avoiding censorship or arrest.
But others have gone much further, and directly called on Mr Xi to stand down.
Despite heavy censorship, news of the demonstrations, videos and pictures have been spreading through social media and messaging apps.
The leading Chinese dissident artist and filmmaker, Ai Weiwei, likened China's strict Covid policies to the country's 1990 public health scandal in the province of Henan where people had been making money by selling blood, which led to hundreds of thousands becoming infected with HIV.
Mr Ai, an outspoken critic the Chinese government, said there were lots of similarities in terms of government attempts to control information.
"A zero-Covid policy only can happen in China or North Korea... and the government never lets people know exactly the truth," he told the BBC's PM programme.
"The economy is collapsing, young people have no jobs and students have no future, the graduates cannot find a job so that creates a lot of reason for these kind of protests."