Concerns are mounting for a Taiwan-based book publisher believed to have been detained in China, in a case that has echoed the disappearances in 2015 of five Hong Kong booksellers.

Li Yanhe, also known by the pen-name Fucha, reportedly travelled to Shanghai last month to visit relatives but has been uncontactable since Thursday. His alleged detention was first reported by Bei Ling, a Chinese writer and activist, who said on Facebook that he had been told by various sources that Li had been arrested by authorities in Shanghai.

Taiwan’s government has said it is monitoring the situation. Last week, a mainland affairs council spokesperson, Jan Jyh-horng, said Li was “safe” but declined to give further details, citing calls for privacy from his family. Taiwan’s premier, Chen Chien-jen, said the government was providing care and assistance to Li’s family.

Bei later took down his Facebook post reportedly upon request of Li’s family, but the alleged detention has sparked concern in Taiwan and in east Asian academic and dissident circles. Under the rule of China’s leader, Xi Jinping, crackdowns on dissenters, human rights groups, and critics have intensified.

Gusa is known for publishing books that are critical of the Chinese Communist party (CCP) or are politically sensitive, including about the Tiananmen Square massacre, human rights abuses of Uyghurs in Xinjiang, and corruption within the CCP.

Li was born in China but relocated to Taiwan in 2009, where he established Gusa Publishing. Colleagues at Gusa have said Li had since obtained citizenship of the Republic of China (Taiwan’s formal name), and was seeking to renounce his Chinese citizenship within the requisite three months under Taiwan law. Taiwan media also cited government officials as saying Li was being treated as a Taiwan national.

The case has drawn comparisons to the detention of five booksellers connected to Hong Kong’s Causeway Bay Books, a seller of numerous critical, political and gossipy titles that had been banned by the CCP. In late 2015, the five were “disappeared” from various locations in Hong Kong, mainland China and Thailand, re-emerging later in Chinese detention.

One, Gui Minhai, remains in detention, and in 2020 was sentenced to 10 years on charges of “illegally providing intelligence overseas”. Another, Lam Wing-kee, skipped bail in Hong Kong in 2016, later fleeing to Taiwan where he has since re-established the bookstore in Taipei.

Lam told the Guardian on Monday that Chinese authorities would be treating Li as a Chinese national, whether or not he had renounced his citizenship to obtain Taiwanese citizenship.

“From the point of view of mainland China, they think you’re from where you were born,” Lam said. “Li published some books in Taiwan that violated the laws of his own country. This is a more serious situation … Publishing these books is a risk. And it is an important warning to other Taiwanese publishers.”

Supporters including the Gusa publishing house, where Li is editor-in-chief, PEN America, and dozens of writers, academics and activists have all voiced concerns for his safety.

“Li is not the first publisher to be detained by China, which is also the world’s largest jailer of journalists,” said the TFCC on Monday, calling on Beijing to respect media freedom and release “all unjustly imprisoned media workers”.

On Saturday, a group of more than 40 Asia-focused writers, media workers and academics joined Gusa Publishing on a statement calling for his release. It said Li had not had access to lawyers or family members and communication was restricted, according to a report by Taiwan’s CNA.

“In Taiwan, freedom of speech and publication, and academic freedom are like the air we breathe. They are part of daily life for every reader, every author, every translator and every editor,” said the statement.

“Under Fu Cha’s leadership as editor-in-chief, Gusa’s books have been very popular with Chinese-language readers around the world for their diversity and the inspiration they provide. We believe Fu Cha has not committed any crime in utilising these freedoms.”