Chinese authorities are detaining and interrogating dissident Twitter users in what seems of be an escalation of its internet censorship, The New York Times reports.

While Twitter is officially not available in China, a small percentage of Chinese internet users access it using software to circumvent the Great Firewall.

The Times interviewed nine people who've been questioned by police over their tweets, including a human rights activist who was manacled to a chair.

Chinese Twitter users have been detained, interrogated, and threatened for their tweets, The New York Times reports.

Twitter, like many internet platforms including Facebook and Google, is not available in China. Nonetheless, a small percentage of Chinese internet users circumvent the Great Firewall using software to access the site.

Now it seems that Chinese authorities are cracking down.

The Times spoke with nine Twitter users who have been questioned by the police, and reviewed a recording of a four-hour long interrogation. Officers showed people printouts of their tweets complaining that they were critical of the government or of President Xi Jinping, and advised them to take down their tweets or delete their accounts.

Those interviewed told the Times that officers sometimes resorted to threats. An activist with a Twitter following of 8,000 said he was interrogated for eight hours while manacled to a chair. Afterwards, he signed a promise to stay off Twitter.

Read more: Google is likely to end its efforts to build a censored search engine for China, says report

A construction company employee told the Times that he was interrogated for 20 hours over a dissident cartoon he posted. He was released, but officers later showed up at his work demanding he sign a document saying he had disturbed the social order. After he signed, they showed him another document saying he was to be detained. He then spent two weeks in a cell watching propaganda videos.

"We're like lambs," he told the Times in a phone interview. "They're taking us one after another. We have no ability to fight back."

Another human rights activist, Wang Aizhong, told the Times: "If we give up Twitter, we are losing one of our last places to speak."

He said that police demanded he delete tweets critical of the government. He refused, but last month Twitter started sending him messages with backup codes to his account and he found 3,000 of his tweets had been deleted. Wang believes they were taken down by state-affiliated hackers.

A Twitter spokeswoman declined to comment on the government campaign when contacted by the Times. Business Insider has contacted Twitter for comment.