Every year in late May, Hu Jia is taken on a mandatory holiday to Qinhuangdao, a port city almost 200 miles from his home in Beijing. He is accompanied by police on walks in the park or by the sea and is always in view of a minder. Hu returns to the capital only after 4 June, the anniversary of the Chinese government’s crackdown on pro-democracy protests in Tiananmen Square.

Hu, one of China’s most prominent political activists, has been under house arrest for years in part for attempting to commemorate the anniversary of the crackdown, one of the most notorious incidents of state violence against activists in living memory. He still maintains hope that democracy will come to China in his lifetime.

“I won’t change, because this is based on feeling,” he said. “I don’t believe the Chinese Communist party is made of iron. I have never lost faith. I don’t think the power of evil can last for ever. It won’t.”

This June marks the 30th anniversary of the crackdown, in which about 3,000 students, workers and other demonstrators are thought to have died. Another estimate put the figure at 10,000, according to a secret British diplomatic cable released in 2017.

Hu is one of many Chinese campaigners who are placed under tight surveillance in the days leading up to and after each anniversary. Every year, Chinese authorities launch an extensive “stability maintenance” campaign in which activists, critics of the government and outspoken parents of those who died in the crackdown are “travelled” to locations outside of Beijing or placed under house arrest. Social media is scrubbed of terms and images referring to the protests. Internet users sometimes find that searches even for words such as “today” are blocked.

Some expect the campaign to last longer than usual this year because of the significance of the anniversary. Gao Yu, a journalist who attended the protests in 1989, said controls on her had been more severe than in previous years. She was placed under house arrest for almost three months from 17 January, the anniversary of the death of the reformist leader Zhao Ziyang, who opposed sending tanks into Beijing, and she expects to be “travelled” next week and again over 4 June, probably for a week.

Zhang Xianling, whose son was killed in the crackdown, said police stationed themselves outside of her house on the anniversary of Zhao’s death and also visited her on 4 May, the anniversary of a student uprising in 1919.

But activists say there is little work left for authorities to do, as there are few people left to speak up about the day. Over the last six years China’s leader, Xi Jinping, has overseen a clampdown on almost all aspects of civil society, from rights lawyers to university students lobbying for workers’ rights.

“Thirty years since the Tiananmen massacre, human rights in China right now is at its worst level and grassroots activism is in its toughest period,” said Yaqiu Wang, a China researcher at Human Rights Watch.

Surveillance infrastructure ranges from facial recognition to cameras to real ID registration for social media use, transportation or hotels. Zhang and Gao say their phones have long been bugged.

“In general, the control is more comprehensive now,” said Ai Xiao Ming, an activist and documentary film-maker who has been banned from leaving the country for the last 10 years. “‘Stability maintenance’ has been institutionalised. There are many methods.”

Campaigners who have spoken up have been punished. Four men who made liquor bottle labels that included the date of the Tiananmen crackdown were given jail sentences this year, after three years in pre-trial detention. “They have created the condition that whoever dares to stand up will be severely punished. They have paved the way for this year, because they know that the 30th anniversary means a lot to people,” said Hu.

The anniversary comes at a challenging time for the Chinese leadership, which is locked in a bruising trade war with the US and facing security concerns about its telecoms firm Huawei and growing criticism over the treatment of Muslim minorities in Xinjiang.

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“The Chinese government is very nervous because the internal and external situations are both not beneficial to the Chinese Communist party, its prestige and its leaders,” said Pu Zhiqiang, a human rights lawyer who was detained for trying to mark the 25th anniversary of the Tiananmen protests. “They are under a lot of pressure. Everyone feels the pressure, which spreads from the government to society.”

Unlike the students in 1989 calling for democratic reform, most rights advocates in China now are pushing for more modest goals such as equal education, labour protections, housing rights or adherence to China’s constitution and legal code.

“Many defenders are not even taking an explicitly pro-democracy or political stance, but the government treats activists calling for protection for disadvantaged and marginalised groups as enemies of the state,” said Frances Eve, deputy director of research at Chinese Human Rights Defenders.

Despite government efforts to erase the memory of 4 June, it is hard to suppress. This year memorials are planned around the world, including in neighbouring Hong Kong. “Whether among the people or within the government, June 4th is always there,” said Pu. “Many people still haven’t forgotten about it.”