Three Chinese volunteers who helped to publish censored Covid-19 articles on Github, the world’s largest open-source website, have been detained by police at an unknown location, according to a source close to them.

The trio – Cai Wei, his girlfriend, a woman surnamed Tang, and Chen Mei – were contributors to a crowd-sourced project known as Terminus2049 that began in 2018 and collected articles that had been removed from mainstream media outlets and social media.

Microsoft-owned Github lets programmers collaborate on code, but has increasingly become a haven for Chinese activists who want to circumvent the Great Firewall to publish censored content.

View photos Chen Mei, another one of the missing trio. Photo: Handout More

There are other archives on GitHub that collect coronavirus-related articles and personal accounts found on mainstream and social media, and some of these projects say they hope to keep a record to help people better “understand the epidemic and the people affected by it”.

Terminus2049 appeared to be blocked in mainland China on Saturday.

The three Beijing-based volunteers went missing on April 19, the source, who declined to give her name for fear of retaliation, told the South China Morning Post. Their families and friends then called the police, who initially denied knowledge of their whereabouts.

“About five days later, the families of Cai and Tang received official notices from the Chaoyang district bureau of the Beijing police,” the source said. “During the first few days they did not admit they took them.”

According to the notices, Cai and Tang were being kept under police surveillance at an unnamed location for “picking quarrels and provoking trouble”.

Chen’s family has not yet received any notification from the police.

“They had regular contact with their families and friends. Now that they have been taken, their families and friends are distraught beyond imagination,” the source said.

The Chaoyang police bureau could not be reached for comment.

Among the articles and personal accounts published by the project, one of the most well known is an interview with Ai Fen, a whistle-blower doctor at the Wuhan Central Hospital. The article was published by China’s People magazine in early March but was removed within hours.

Ai, who said she had been muzzled by the authorities for raising the alarm without permission at the start of the outbreak, posted an image of a diagnostic report on social network WeChat on December 30, showing that a patient had a pneumonia infection caused by a Sars-like coronavirus.

Some of the information she released was also shared by Li Wenliang, the doctor who was detained by the authorities and who later died from Covid-19.

After the removal of Ai’s article, angry members of the public published dozens of different versions on social media, using emojis, code words and different languages – even invented ones such as Elvish and Klingon – to bypass the censors.

View photos Citizen journalist Li Zehua re-emerged after going missing for two months. Photo: YouTube More

Earlier this week, citizen journalist Li Zehua re-emerged after going missing for two weeks. He said he had been held in a quarantine centre in Wuhan before being sent to isolation in his hometown.

But the whereabouts of Chen Qiushi and Fang Bin, two other citizen journalists who disappeared in Wuhan in early February, remain unknown.

Chen, a lawyer and citizen journalist, arrived in Wuhan, the epicentre of the outbreak in China, on the last train before the lockdown.

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