Chinese authorities have stepped up surveillance and harassment of government critics as part of a crackdown on dissent ahead of the Communist party’s upcoming 20th congress, its key political gathering.

Since mid-September, numerous activists and petitioners seeking to lobby the government have been detained or put under house arrest across China, while many human rights lawyers have been intimidated, harassed and followed by agents. They say authorities, wary that their criticisms of the government could lead to social discontent and threaten the regime, are pulling out all the stops to silence them ahead of the twice-in-decade event, set to start on Sunday.

Xi Jinping is expected to gain an unprecedented third term as a party leader at the congress, sparking the highest level of security to keep any potential disruption in check.

“Every morning, the police would call me to check my plan for the day. They order me not to go anywhere, see anyone or say anything to them,” said one lawyer who was disbarred and had his law firm closed for defending politically sensitive cases. “The message is clear: ‘We are watching your every move.’”

The lawyer, who requested anonymity for fear of reprisals, said Chinese social media platforms block all his posts and even when he skirts the firewall to post on Twitter, local police summon him and issue warnings on posting politically sensitive content.

On Wednesday, lawyer Yu Wensheng, who has spent four years in jail, was barred from going out by security staff at his housing compound. He said police warned him against going to foreign embassies, talking to journalists, or posting on Twitter ahead of the congress. “I guess they’re trying to scare us,” he said, insisting he would not back down.

Another rights lawyer, Wang Quanzhang, who was jailed on subversion charges for defending activists, said authorities had stepped up surveillance on his family in recent days. This week, more agents were deployed to watch and follow his family when they go out and police warned him against airing his opinions, he said. “I guess the surveillance will escalate in the next few days,” he said.

Veteran lawyer Li Heping also received the same treatment. His wife, Wang Qiaoling, said that since mid-September, plainclothes policemen had been guarding their housing compound and police cars follow them whenever they go out. “It is an intimidation strategy to frighten us,” she said. Lawyer Xie Yanyi said security cameras around his home had all been upgraded in recent days while police cars guard his compound. Lawyer Jiang Tianyong remains under tight surveillance in his home town in rural Henan with little means of communication with the outside world.

Prominent writer Gao Yu who is in fragile health, cannot be reached. Veteran activist Hu Ju said on his WeChat account on Thursday that he has been forced to leave Beijing for around 10 days and fears that the stringent Covid measures may delay his return to tend to his sick mother.

A number of petitioners across China who had planned to bring their grievances to Beijing have been forcibly taken from their homes and detained. Police detained many staying near Beijing and forcibly sent them back to their home towns for detention. One petitioner told Radio Free Asia that police set up checkpoints at railway stations and on roads to block them from entering Beijing. Once found, they would be sent back to their home towns, where they would be detained.

Minsheng Guancha (or Civil Rights & Livelihood Watch), a website that reports human rights violations in China, has documented dozens of cases of activists and petitioners being confined to their homes, forcibly repatriated and detained ahead of the party congress. Many have been detained for up to 15 days on the vaguely defined charge of “picking quarrels and provoking trouble”.

The Chinese authorities have long used blanket charges such as “provoking trouble” to target those seen as a thorn in the side of the government.

Just two weeks before the congress, the Ministry of Public Security announced that its “100-day” crime busting operation, which started in June, had resulted in 1.43 million people being arrested.

The head of the operation, Qiu Baoli, said the campaign, implemented with a “heavy fist”, laid a “solid foundation” for safeguarding the political meeting.

Observers say the crackdown on dissidents and activists would have fallen under this campaign because they are often accused of “picking quarrels and provoking trouble” for protesting.

But even such an extensive operation did not manage to completely eliminate voices of dissent. On Thursday, a rare protest in Beijing against the Communist party and its policies stoked political tensions just three days before the congress which will re-anoint Xi as the party leader for the next decade.

Photos and videos emerged on social media show two banners hanging from an overpass of a major thoroughfare in the northwest corner of the Chinese capital. Plumes of smoke could be seen billowing from the bridge. “We want food, not PCR tests. We want freedom, not lockdowns. We want respect, not lies. We want reform, not a cultural revolution. We want a vote, not a leader. We want to be citizens, not slaves,” reads one. A second banner called for a boycott of schools and strikes and the removal of Xi.

Although images and keywords related to the protest were censored by internet police, many people made oblique remarks referring to the incident on Chinese social media platforms. “It is strange when the word ‘brave’ has become a sensitive keyword,” said one on WeChat. On Twitter, which is unaccessible from China unless one skirts the firewall, the images and videos went viral and drew a large amount of supportive comments. It appeared to have also energised the exiled Chinese dissident community, with some holding an online seminar analysing the significance of the protest .

Meanwhile, internet censors have also pulled out all the stops to police cyberspace, barring many politically sensitive words and phrases, including nicknames of Xi, descriptions of the stormy weather, and even the bear head emoji – as Xi has been compared to the cartoon character Winnie the Pooh – according to Radio Free Asia.

Local authorities have been under extreme pressure to ensure a stable and positive environment in China for the meeting, but have been challenged by widespread outbreaks and growing frustration with the zero-Covid measures. Across China, some people who left Beijing for the Golden Week holiday have reported they have been blocked from returning.

Alerts sent by the mandatory healthcode app informed users they “may have a time and space relationship with the epidemic risk” and must delay their return until risks were ruled out or they had spent seven days in a “low risk” area. About 90% of the country is currently designated medium or high risk, according to China’s government.

Even the air is controlled. On Friday, Hebei province’s iron and steel industry was ordered to halve its output for a week. No reason was given for the order, but China’s government has often limited polluting industries around the time of major events to ensure clear blue skies.