HONG KONG — At 6.49am on Oct 17, not long after the police completed a pre-dawn operation to clear a protest camp in Hong Kong’s Mong Kok neighbourhood, someone posted a call to action on a popular online forum, urging residents to retake the streets.

“Tonight, if you’re a man, let’s revive Mong Kok,” a user calling himself Li Siu-ming wrote on the HKGolden website. “If there are no other options, we will have to blockade the railway station, paralyse the MTR,” he added, referring to the city’s subway system.

There was little to distinguish his posts from others about the pro-democracy demonstrations that have disrupted Hong Kong for more than a month. But the next day, the police demanded user data related to his messages, said HKGolden’s manager.

Hours later, officers arrested a 23-year-old man at his home, saying he had incited others online to join the unlawful assembly in Mong Kok, charge at police and paralyse the railways.

In announcing the arrest, police spokesman Hui Chun-tak made a sweeping assertion: It is a crime in Hong Kong to post messages calling on people to attend the protests. “Inciting others to commit criminal acts on the Internet is illegal,” he said.

The warning, along with a refusal to disclose more details about the case, has heightened fears that the authorities have begun to police the Internet using methods more often associated with the security forces in mainland China, where Web censorship is routine and a crackdown on online dissent has been under way for over a year.

The ex-British colony has enjoyed a high degree of autonomy since its return to Chinese rule in 1997, retaining a Western-style legal system and protections for freedom of speech. But concern about China’s rising influence and anxiety that Hong Kong is becoming more like the rest of China have helped fuel protests demanding open elections for the city’s next leader.

“The protests are about protecting ... values and freedoms from mainland encroachment,” said Ms Maya Wang, a Hong Kong-based researcher for Human Rights Watch, adding that the arrest raises questions precisely about these values being eroded.

Given the protests, she said, it is even more urgent for the government to clarify why this act of law enforcement is not encroaching on these freedoms. The police have declined to provide the exact language that prompted the arrest or confirm any link to the messages posted on the HKGolden forum.

But Mr Joe Lam, the site’s chief executive, said officers had demanded that he provide them with the Internet Protocol addresses and messages associated with Li Siu-ming’s account.

Besides the call to paralyse the subway system if needed, the user urged protesters to force police to use force when retaking the Mong Kok site.

After protesters succeeded in re-establishing the camp, he suggested online at 1.57am on Oct 18 that they charge Lung Wo, a street outside the Hong Kong government’s office. The next day, he said officers had gone to his home and arrested him for messages supporting the protesters.

The police have identified the suspect only by his surname, Tam, and said he had been released on bail pending an investigation.

Mr Tam initially sought the help of a group of lawyers and volunteers linked to the protest organisers; they said his full name was Tam Hiu-fung.

In a private message on the forum, the user confirmed his name was Tam Hiu-fung. He said on the phone: “I’m an ordinary Hong Kong youngster. I just want to do something for Hong Kong.”

In Hong Kong, the government can use an arrest as an early step in a criminal inquiry, letting the police gather evidence before deciding with prosecutors whether to file charges. But even if they drop the case, the arrest may have served a purpose. “It scares people away,” said Mr Charles Mok, who represents the IT sector in the Legislative Council. “(People) are worried ... they would get in trouble posting messages,” he said. THE NEW YORK TIMES