But the Beijing-based lawyer and online commentator made his comeback on Sunday when a video he said was made in the northern coastal city of Qingdao on October 2 was shared on Weibo.

He said that after being asked to give an account of his trip to Hong Kong, he was questioned, recorded, and “criticised and educated”.

“Even yesterday, I was taken away again by the police,” he said.

Although the film appeared on Weibo, it was sourced from Chen’s new YouTube channel. It is one of three he has uploaded to the channel since Thursday.

In the second clip, Chen lashes out at the growing list of topics that Chinese people are banned from talking about.

“In a … mature country, the problem is not that there are people talking about ‘sensitive topics’. The problem is the existence of such ‘sensitive topics’,” he said.

The only way to change that was for people to keep discussing them, he said.

Chen’s third video takes aim at the political climate in mainland China. He said that when he was questioned about his trip to Hong Kong, all the officials were interested in was his political standpoint.

“No one cared about the facts. My stance was all they cared about,” he said.

“We always say that some members of the public are unaware of the truth and can be easily duped. But I’m concerned that there are also officials who are unaware of the truth and can just as easily be manipulated.”

Chen’s re-emergence on YouTube – his channel was created on October 5 – is indicative of his determination to fight the censorship he faces at home. The platform, like Facebook, Twitter and Instagram, is blocked in mainland China, but can be accessed with the help of a virtual private network to bypass the country’s tight censorship, or Great Firewall of China.

Beijing has maintained a tight grip on the online discussion of the anti-government protests in Hong Kong, and material that supports or empathises with the movement is swiftly removed by the censors and social media accounts are frequently blocked.

There have been reports of other mainlanders being detained and questioned after travelling to the city to show their support for the protesters or report on their activities.

Chen said in the first film that on his return he agreed not to release any videos before the October 1 celebrations, but now that date had passed he was ready to speak out once more.

“Since freedom of speech is a basic citizen’s right written into article 35 of the Chinese constitution, I need to persist because I think this is the right thing to do, no matter how much pressure and obstruction [I] encounter,” he said.

Over the past month, all of Chen’s social media accounts – on Weibo, messaging platform WeChat and Douyin, a popular app for sharing short videos – had been shut down by the authorities, he said.

He said he did set up new accounts on Douyin, but as soon as the censors saw his face in the films they were closed down.

“It’s your job to censor me,” he said in a message to Beijing. “But it’s my right to insist on speaking out.”

Xu – who sparked his own controversy in 2017 when he set about debunking the claims of China’s traditional martial artists – has also been questioned by police and had his social media accounts shut down over his comments about Hong Kong.

“Among all the people who voiced support for me, he was the only one who was willing to show his face in the videos,” he said.

Chen ended his latest film with a message for Hong Kong.

“It’s been a month since I returned from Hong Kong, where things have changed a lot,” he said. “I hope Hong Kong’s chief executive, government and citizens can come to terms with each other and find a solution that benefits everyone.”

He did not immediately respond to requests for comment.