A friend of Xu told The Guardian that the professor was placed under house arrest after he returned to Beijing following the Lunar New Year celebration.
"They confined him at home under the pretext that he had to be quarantined after the trip," the friend said. "He was in fact under de facto house arrest and his movements were restricted."
The Guardian reported that guards were patrolling outside Xu's home last week, though they have since left. Xu remains incommunicado.
The law professor's name is notably absent from China's Weibo social network.
I understand that Professor #XuZhangrun is effectively under house arrest and barred from social media & internet. I am sharing his essay 'Viral Alarm: When Fury Overcomes Fear' to help keep his message alive. Pleases share if you can. https://t.co/mwyumjfA3B pic.twitter.com/3qJBe5DoFs
— Anna E. Ridgway (@AnnaERidgway) February 16, 2020Xu's access to the internet has been cut off, and his social media account on China's WeChat messaging platform was shut down.
According to The Guardian, many of Xu's friends have been unable to get in touch with him for days. One of the professor's friends anonymously reported that they had managed to text him but feared Xu was under surveillance.
"He has not directly responded (to my queries) but just told me not to worry," the friend told The Guardian.
Xu's essay ended with an ominous acknowledgement: "I can now all too easily predict that I will be subjected to new punishments; indeed, this may well even be the last piece I write."
This isn't the first time Xu has been punished for "speech crimes," according to his essay.
In 2018, he was placed under investigation by Tsinghua University after publishing another essay criticizing Xi Jinping.
"I was suspended from my job as a university lecturer and cashiered as a professor, reduced to a minor academic rank," he wrote, adding, "my freedoms have been curtailed ever since."
Another activist, Xu Zhiyong, published an article on social media this month urging Xi Jinping to step down.
The recent post from Xu, a civil-rights lawyer and public intellectual, called out the Chinese president for his "inability to handle major crises," according to the South China Morning Post.
Xu previously served four years in prison for his legal activism. He was arrested again on February 15 after being on run for two months following a police crackdown on a meeting of human-rights lawyers and activists that he attended in Xiamen.
Doctor Li Wenliang was censored for warnings he shared on social media.
The WeChat message Li sent to his medical-school contacts on December 30 told them about seven patients with an unknown virus. They had all worked at or visited the Huanan Seafood Wholesale Market.
The same day, the Wuhan Municipal Health Commission published a notice warning that some people had contracted a type of pneumonia, possibly at the market. But the commission said "organizations or individuals are not allowed to release treatment information to the public without authorization," CNN reported.
Screenshots of Li's message had already gone viral, though.
"When I saw them circulating online, I realized that it was out of my control and I would probably be punished," Li told CNN.
Four days after sharing the message, Li was summoned to a police station. Authorities told him that his warning was illegal and had "severely disturbed the social order," the BBC reported.
According to the BBC, the letter he was told to sign read: "We solemnly warn you: If you keep being stubborn, with such impertinence, and continue this illegal activity, you will be brought to justice — is that understood?"
Beneath that, Li wrote, "Yes, I do."
Li was not detained, and he returned to work.
After his release, Li unknowingly treated a woman infected with the coronavirus. Two days later, he checked himself into the hospital after showing symptoms. He died less than a month later.
While sick in the intensive care unit, Li continued to post on his Weibo account.
"I was wondering why [the government's] official notices were still saying there was no human-to-human transmission, and there were no healthcare workers infected," Li wrote on January 31 from his hospital bed, according to CNN.
Days before his death, he told the New York Times that officials could have done better at sharing information about the coronavirus at the beginning of the outbreak.
"I think it would have been a lot better. There should be more openness and transparency," he said.
Following Li's death, Chinese lawyer and citizen journalist Chen Qiushi went missing.
Chen traveled to Wuhan in late January and uploaded more than 100 posts from Wuhan to his Twitter and Youtube accounts over two weeks. His videos showed overwhelmed hospitals and medical wards.
Chen's friends and family have been unable to reach him since February 6, according to posts on his Twitter account. They say he was forcibly quarantined by Wuhan police. Chen's Weibo account — which had more than 740,000 followers — was shut down on the day of his disappearance, according to his friends and family.
On January 30, Chen uploaded a video to his YouTube channel in which he said police had called him wanting to know where he was and had questioned his parents, according to the Associated Press.
"In front of me is the virus, and behind me is the legal and administrative power of China," he said in the video. "Even death doesn't scare me! Do you think I'm scared of the Communist Party?"
Chen's mother uploaded a video onto Chen's Twitter account after his disappearance, begging for help to find her son.
The Wuhan and Qingdao city police said they had no information about Chen's whereabouts when contacted by CNN.
陈秋实妈妈呼吁网友寻找秋实下落！陈秋实昨天说要去方舱医院，从晚上七八点到凌晨两点都处于失联状态。#WuhanCoronavirus #Wuhan #WuhanChina pic.twitter.com/FtrGjr495H
— 陈秋实（陳秋實） (@chenqiushi404) February 6, 2020This wasn't the first time Chen has been silenced by Chinese officials.
Chen traveled to Hong Kong in August to report on the protests there. After his trip, all of his social media accounts were deleted, he told Quartz in early February.
So this time, he added, "I gave my overseas friends all the passwords to my social media accounts like YouTube, and if I don't contact them for 12 hours they will change the passwords."
One of Chen's friends, Xu Xiaodong, posted an update on YouTube February 9 saying Chen had been "detained in the name of quarantine" for two weeks, despite showing no symptoms of the virus. According to the AP, Xu also said on Twitter that day that no one had been able to get in touch with Chen in quarantine.
"I risked my life to post the videos," Chen told Quartz, and added: "If I get arrested they could force me to delete all my videos on YouTube and Twitter, and that would be a great blow to me."
Blogger Fang Bin also got a call from the police in Wuhan. Authorities confiscated his laptop from his home on February 1 and brought him in for questioning. Fang filmed the encounter.
Fang told The Los Angeles Times that authorities ordered him to stop posting "rumors" that would "spread panic" online.
The police released him the next morning. Fang posted a video suggesting that he was released because of the outpouring of support for his freedom on social media.
A video Fang posted on February 1 showed a hospital in Wuhan where eight body bags were being loaded onto the back of a truck. The footage also showed an overwhelmed medical clinic. It went viral.
After his release, Fang continued posting videos from hospitals across Wuhan.
"This pneumonia we see today, this Wuhan flu, it's both a natural disaster and a man-made problem," he said in one of his videos. "That's because they've covered up the facts. They muffled Li Wenliang for telling the truth."
Bilingual titles added. 8 bodies in 5 minutes! More are lying inside to be moved out. Somebody secretly shot this video from No. 3 Hopital in #Wuhan during #coronarovirus #武汉肺炎
字幕版
某網友秘訪武漢第三醫院，五分钟功夫就見到八具屍體拉走去火化場，而且里面还有。 pic.twitter.com/VBS6U7HIWW
Fang was arrested on February 10.
He refused to leave his home, according to Vice, so firefighters broke down the door after police surrounded the apartment.
The last video Fang posted to his YouTube channel came on February 9. In it, he repeated again and again: "All citizens resist, hand power back to the people!"
- Read more about the coronavirus:
- Everything we know about the deadly Wuhan virus sweeping across China
- Whistleblower doctor Li Wenliang, who was censored after sounding the alarm about the coronavirus, has died in Wuhan
- One of the largest study of coronavirus patients so far suggests it could take up to 24 days after exposure for symptoms to show
- There's a good chance the Wuhan coronavirus will never disappear