Protesters in Hong Kong are attempting to hide their identities amid mass protests over a controversial extradition bill.

Protests began Sunday and continued Tuesday night and into Wednesday. Clashes between protesters and police turned violent on Wednesday.

Debate on the bill was slated for Wednesday morning but was postponed. The police commissioner called the June 12 protests a "riot."

INSIDER spoke to three human-rights activists in Hong Kong who described the lengths protesters are going to conceal their identities.

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Protesters in Hong Kong are going to great lengths to hide their identities from the government as they join mass protests over a controversial bill being considered by the Legislative Council.

Over a million Hong Kong residents — nearly 1 in 7 people there — protested last Sunday, according to the Civil Human Rights Front, which organized the event. Police estimated the number was closer to 240,000.

The territory is experiencing one of the largest demonstrations in its history in response to a measure that would allow extradition of Hong Kong residents to mainland China.

Hong Kong Chief Executive Carrie Lam said Saturday afternoon that her government had heard calls to "pause and think" and that the bill was being suspended without a date for "the next step forward."

Demonstrators appeared ready to continue, however, with renewed calls for protests on Sunday and Monday.

Hong Kong Chief Executive Carrie Lam at at a news conference, June 15, 2019. REUTERS/Athit Perawongmetha

Hong Kong was handed over to China from the British in 1997 and was allowed to keep its criminal justice system, which differs from that of the mainland.

Though Hong Kong has been able to maintain a certain degree of autonomy from the mainland, China has been slowly tightening its grip on the city as the 2047 expiration of Hong Kong's Basic Law — the region's constitutional framework, which grants certain exemptions from China's communist system — draws nearer.

China takes great measures to stifle dissent through mass detention, censorship, threats, and kidnapping, and critics of the bill say that extradition to China could subject Hong Kong residents to such unjust practices.

The protests, began on Sunday and continued Tuesday night and into Wednesday. Prior to Lam's announcement, more had been planned for Sunday.

Hong Kong protesters have been especially cautious about revealing their identities out of fear of arrest or reprisal. Rioting is considered a serious offense under Hong Kong law and carries a maximum sentence of 10 years. The police commissioner called the June 12 protests a "riot."

Demonstrators near the Legislative Council in Hong Kong, June 12, 2019. AP Photo/Kin Cheung, File

"Some people who participated in this protest have already been arrested, but if the law passes, we fear that even more will be at risk," Timothy Loo, a human-rights advocate based in Hong Kong who participated in the protests, told INSIDER.

Loo added that people are being particularly careful to conceal their identities from being linked to current protests in the wake of 2014's Occupy Central demonstrations, the last protests of this size in Hong Kong. Those protests called for fully democratic elections and distance from Chinese oversight. Several leaders of the 2014 protests, including student activists, professors, and former lawmakers, were handed prison sentences for their involvement.

"We're already seeing the police cracking down — they've taken students from university dorm rooms and injured patients from hospitals," he said. "I think people are trying to be very cautious this time around."

Here's what protesters have done to obscure their identities.

Masks to protect from tear gas and to conceal faces

Protestors wear masks and helmets to protect their identities, near the Legislative Council in Hong Kong, June 12, 2019. AP Photo/Kin Cheung

Many protesters wore face masks, hats, and goggles during the protests. The action was twofold — it protected people from tear gas and rubber bullets shot by police at crowds on Wednesday, and it obscured the identities of protesters from authorities amid increased concern over photos taken of the demonstrators and facial recognition software.

Activists at the heart of the protests were seen passing out medical masks, umbrellas, goggles, and hats as part of a collective effort.

—Alice Su 苏奕安 (@aliceysu) June 12, 2019

Protesters have also been wary of speaking to journalists or revealing their names publicly; some of the activists INSIDER spoke to for this story requested anonymity out of concerns for their safety.

On Thursday, reporters seemed to adopt the protest uniform and appeared at a press conference wearing helmets, masks, and glasses.

—TicToc by Bloomberg (@tictoc) June 13, 2019

Paper tickets for the subway

Photos circulating online showed longer-than-normal lines to buy single-use paper tickets for the territory's transit system.

Two human-rights advocates based in Hong Kong confirmed to INSIDER that many protesters were choosing to use single-use tickets as opposed to the Octopus cards, which can be connected to personalized information like their name, photo, or bank account details along with reward points for shopping.

We're afraid of having our data tracked," one woman protester told Mary Hui, a Hong Kong-based journalist for the online news site Quartz.

'Throwaway' SIM cards and encrypted messaging

Three human-rights advocates inside Hong Kong discussed with INSIDER the use of private chats and encrypted messaging services like WhatsApp and Telegram to spread information to journalists and other activists.

On Wednesday, however, Telegram announced it was experiencing connection problems related to a massive cyber attack. Its founder, Pavel Durov, said on Twitter that the attacks were tied to a "state actor" with "IP addresses coming mostly from China." He added that the attacks coincided with protests in Hong Kong.

"Many people were using Telegram for added privacy, but since it was hacked people are being advised to delete the app and turn off location services," Loo said.

Police clash with protestors during demonstrations in Hong Kong in 2014. Reuters/Bobby Yip

The messaging app later tweeted that the situation had "stabilized" and assured users that their data was safe.

The New York Times reported that 22-year-old Ivan Ip, an administrator of a Telegram group sharing information about the protests, was arrested, though he had not taken part in the protests. He was "suspected of conspiracy to cause a public nuisance," The Times reported. He was later released on bail.

Following his arrest, messages urged protesters to use "pay-as-you-go SIM cards or register foreign numbers online to join groups."

One source who declined to be identified also told INSIDER that some protesters were choosing to buy "throwaway SIM cards" to communicate with others in an effort to further hide their identities.

"I'm not, but [I] did clear some of my chat histories," the source said.

Avoiding public hospitals for fear of arrest

An injured cameraman after riot police fired tear gas at protesters outside the Legislative Council in Hong Kong, June 13, 2019. AP Photo/Vincent Yu, File

Activists are urging protesters to avoid public hospitals over fears of arrest by police, who are reportedly stationed outside medical buildings.

On Thursday, reports emerged that at least four people were arrested at public hospitals after sustaining injuries during clashes with police. According to the South China Morning Post, hospital staff notified police of patients who acknowledged they had participated in protests.

Two Hong Kong-based human-rights advocates, who requested anonymity, told INSIDER that messages — purportedly from legal aids — were circulating in private forums and social-media groups, cautioning injured protesters from consenting to having their medical information shared with the police.

INSIDER was sent a copy of the message, but could not independently verify its origin.

"Remember to 'decline' the police request for a copy of the medical report," a message in English and Chinese, obtained by INSIDER over WhatsApp, read.

People are also being warned to avoid public hospitals as police could be stationed there "ready to make arrests," the message read.

What's at stake?

A police officer walks by the words "Love Hong Kong" written with tape near the Legislative Council in Hong Kong, June 14, 2019. AP Photo/Vincent Yu

Video from the protests, which turned violent on Wednesday, shows police firing rubber bullets and tear gas into crowds. Other protesters were pepper-sprayed or blasted with high-pressure water hoses.

Police defended their response to the escalation, saying they were left with "no choice" but to use force against protesters who supposedly charged at police and hurled bricks, metal poles, planks, and barriers at officers on the front lines.

As of Thursday evening, 11 people had been arrested in relation to what police described as "disorderly conduct in public place, unlawful assembly, assaulting police officers and other riot-related offences." Eighty-one people who were injured during the protests were sent to public hospitals, according to Hong Kong's information bureau.

Government offices in the financial district were shuttered through the week, and employees were told to avoid entering their workplace in anticipation of more clashes, though protests had largely diminished by Friday.

On Thursday, bipartisan members of the US Congressional-Executive Commission on China, led by Democratic Rep. Jim McGovern and Republican Sen. Marco Rubio, signaled that they stood behind the people of Hong Kong, introducing legislation that requires the US secretary of state to certify Hong Kong's autonomy from mainland China each year to justify special economic and trade treatment under US law.