Thousands of protesters have taken to the streets of Hong Kong to demand the release of a group of political booksellers they suspect were abducted by Chinese security forces and are being held in mainland China.

Five Hong Kong booksellers – Gui Minhai, Lee Bo, Lui Bo, Cheung Ji-ping and Lam Wing-kei – who specialized in books criticizing China’s Communist party elite have vanished since October.

Beijing has repeatedly refused to comment directly on the case but there is widespread suspicion that the men’s apparent detentions – in Thailand, southern China and Hong Kong – are designed to halt the publication of salacious tomes about the private lives of top party figures.

One source told the Guardian Gui and Lee had been preparing to publish a book about Chinese president Xi Jinping when the disappearances began.

On Sunday afternoon demonstrators gathered outside Hong Kong’s government headquarters – the scene of last year’s umbrella movement pro-democracy protests – carrying placards and banners that read: “Release Hong Kong Booksellers Now!” and “Against political persecution!”

Albert Ho, a Democratic party lawmaker who helped organize the march, said demonstrators wanted the booksellers’ “immediate release”. They were also demanding an explanation from Beijing about the apparent “kidnapping” of Lee Bo, a British passport holder who vanished in Hong Kong earlier this month.

“They owe us an answer,” said Ho. “We are legitimately entitled to be notified about the status of Hong Kong citizens who are being detained in China.”

Sin Chung-kai, another Democratic party politician, said the scandal left the ‘one country, two systems’ model, under which Hong Kong has operated with far greater freedoms than the mainland since handover in 1997, “on the verge of collapse”.

“It is totally terrifying,” Sin told broadcaster RTHK.

The booksellers’ still unexplained disappearances have sparked international condemnation.

On Friday the US said it was “disturbed” by the unfolding scandal. The EU said the continuing lack of information about the booksellers’ welfare and whereabouts was “extremely worrying”, adding: “Respect for freedom of expression underpins all free societies.”

During a two-day visit to China last week, British foreign secretary Philip Hammond said Beijing would be guilty of an “egregious breach” of Hong Kong’s autonomy if the involvement of its agents in Lee Bo’s snatching was confirmed.

Some describe Lee Bo’s suspected abduction as a potentially fatal blow to the former colony’s supposed autonomy from authoritarian China.

Beijing’s continued silence over the case would signal it was “no longer willing to keep [its] promise about ‘one country, two systems,’” said Ho.

“I think they know how serious this matter is in terms of maintaining confidence in the ‘one country, two systems’, not only of the Hong Kong people but also of the international community and the investors in Hong Kong,” he said.

The failure to release the men would be a “catastrophic and devastating” mistake on Beijing’s part, the veteran campaigner added.

The disappearances have also mobilized a younger generation of democracy activist in Hong Kong.

A viral online video in which 19-year-old activist Agnes Chow calls for answers from Beijing has now been viewed more than 945,000 times since it was posted on Facebook at the start of this month.

On the eve of Sunday’s protest one Hong Kong newspaper published extracts from a video and letter, supposedly written by Lee Bo, in which he claims he is “confused and puzzled” by the “fuss” surrounding his situation.

In the letter, which many suspect he was pressured into writing, Lee claimed he had travelled to mainland China in order to resolve “personal issues.”

Originally published by The Guardian