The scholar Guo Yushan, right, is being detained by Chinese officials on charges of “provoking troubles,” his attorney says. In 2012, Guo helped blind activist Chen Guangcheng escape house arrest. Chen’s brother, Chen Guangfu, is at left. (Reuters)

In the latest sign of China’s concern about protests in Hong Kong, books by scholars considered supporters of the demonstrations are suddenly becoming harder to find.

Images of two purported censorship orders — one from a publishing house and the other from China’s main censoring agency — circulated Monday on Chinese social media. The orders directed the removal of books by authors perceived as sympathetic to the protests that erupted late last month.

Chinese officials did not immediately comment publicly on the apparent bans. But they would fit into the broader media squeeze by China, which has blocked reports in state-run outlets about the Hong Kong protests except for the increasingly harsh denunciations by authorities.

It also reflects a larger crackdown on intellectuals that began in the past year and has expanded since the Hong Kong unrest began. The protests there started as a backlash to Chinese plans to vet candidates for Hong Kong elections but have mushroomed into a showdown over the extent of Beijing’s control in the former British colony.

More than 40 have been arrested in mainland China for supporting the protests, according to international human rights groups.

“What on earth is our government trying to do?” wrote Mao Yushi, one of the authors on the apparent blacklist. Censors quickly deleted his online post.

“It really raises doubts. A government that has failed to win the people’s trust, how can it exercise good governance?” added Mao, a liberal economist who said he had heard about the book ban from several people in the government. “How can it maintain stability? How can it win trust from the international community?”

The State Administration of Press, Publication, Radio, Film and Television — China’s regulator for publishing — did not return calls for comment. But the Global Times, a newspaper run by the Communist Party, published an editorial that seemed to confirm the ban.

The future prospect for publication of books by people on the list is grim,” the commentary said. It added: “These people need to navigate carefully.”

According to the censorship order posted online, the newly banned authors include Zhang Qianfan, a Peking University law expert and frequent critic of China’s courts; pro-democracy activist Chen Ziming; Taiwanese writer Giddens Ko; and Hong Kong commentator Leung Man-tao.

Books related to Christianity, Tibetan Buddhism and Islam also will be more strictly controlled, as will historical memoirs, according to the order. Specifically singled out were books by Yu Ying-shih, a prominent Chinese American historian and former professor at Harvard, Yale and Princeton.

Yu had recently voiced support for the “Sunflower” student protest movement in Taiwan this year and encouraged Hong Kong’s students not to give up their movement.

A saleswoman answering the phone at the Guangxi Normal University Press Group confirmed that this week the press stopped selling a book by Yu but declined to give details. The call was transferred to her superiors, who declined to comment.

On Monday, China’s biggest online booksellers already were listing several books that appeared in the alleged orders as out of stock.

As Hong Kong protesters have defied calls to leave the streets, Chinese authorities have stepped up pressure on prominent — or even potential — backers of the challenge to Beijing’s authority.

Officials recently detained Chinese scholar Guo Yushan, most well-known for helping blind activist Chen Guangcheng escape house arrest in 2012 and seek shelter at the U.S. Embassy.

Guo has been held on charges of “provoking troubles,” according to his attorney. While Guo has long advocated for human rights, he had not made any public comments about the Hong Kong protests.

Several artists and writers have been detained as well, including Beijing dissident poet Wang Zang, who was arrested Oct. 1. A few days earlier, his wife, Wang Li, said her husband had posted a photo on Twitter of himself raising his middle finger while holding an umbrella — an item that has become a symbol of the Hong Kong protests.

There are fears that the pressure eventually could extend even to student protest leaders in Hong Kong, which still enjoys many freedoms that mainland China does not.

Agnes Chow, who acted as spokeswoman for a high school student group, said in a written statement that she was resigning.

“I am only 17, facing unbearable pressure, I feel extreme desperation and tiredness. I hope you could respect my decision,” she said.

Simon Denyer in Hong Kong and Liu Liu in Beijing contributed to this report.