Like thousands of Hong Kong natives living abroad, Stan ­Cheung had been following the anti-extradition protests in his homeland closely. On June 12, as he scrolled through Facebook videos of police unleashing tear gas and rubber bullets on protesters, the 26-year-old software engineer from Northern Virginia decided he needed to do more.

He asked his boss for permission to work remotely and bought the earliest ticket he could find out of Reagan National Airport. Two days later, just hours after arriving and dropping off his bags at his brother’s apartment, Cheung joined 2 million people in Hong Kong for the largest protest in the city’s history. Demonstrations quieted this past week but resumed in force Friday.

“I knew I couldn’t just sit behind a monitor,” Cheung, who lives in Reston and has been in the United States since 2012, said in a telephone interview. “I didn’t want to be a free-rider and watch my friends fight for freedom for me.”

The overseas Hong Kong community has mobilized in historic numbers since protests erupted this month against a controversial extradition bill that would allow Hong Kong authorities to hand over to China people charged with crimes. Opponents call it a dangerous overreach of Beijing’s authority over the former British colony.

Few have gone to such lengths as Cheung, but in dozens of cities in the United States, Europe and Australia, protests have been organized in solidarity with the demonstrators in Hong Kong.

Anna Yeung-Cheung, a professor of biology at Manhattanville College in Purchase, N.Y., immigrated from Hong Kong in 1987 and is a coordinator for the Facebook group Global Solidarity for Hong Kong. The professor, 54, said protests abroad have largely mirrored the “leaderless” movement in the city itself, with pockets of citizens voluntarily organizing events.

In New York, more than 1,500 turned up for a June 9 march from Times Square to the Chinese Consulate. Two protests in the District, where the Hong Kong community is smaller, each drew around 60 people.

Former residents of Hong Kong who live in the Washington area have followed the protests in their homeland closely, said Kak Wong, 27, a graduate student at the University of Maryland at College Park. Many have stayed up through the night to monitor developments on social media, he added, and some are active in private chat groups being used to gather and distribute information for protesters back home.

The overseas community took similar action during Hong Kong’s“Umbrella Revolution” in 2014, but not on this scale, said Jeffrey Ngo, chief researcher for the pro-democracy movement Demosisto. Their recent efforts have raised the profile of the anti-extradition movement, he said, and spurred lawmakers elsewhere in the world to pressure Hong Kong officials to withdraw the bill.

“In rallies in Taiwan and Tokyo, we’re seeing participants that aren’t just overseas Hong Kongers but actual Japanese and Taiwanese citizens,” said Ngo, a 23-year-old PhD student at Georgetown University. “What we’re seeing is how the Hong Kong diaspora has influenced local communities to support our cause.”

On Wednesday, House Speaker Nancy Pelosi (D-Calif.) told reporters she would back bipartisan legislation requiring the Trump administration to affirm Hong Kong’s rights as a semiautonomous region of China. Lawmakers in Canada, Japan and Britain have also criticized the extradition bill.

After days of protests, Hong Kong’s chief executive, Carrie Lam, suspended the bill and later apologized for the “anxiety” caused to citizens. But activist groups are not satisfied. They have threatened further protests if the government refuses to withdraw the bill entirely and accede to other demands.

Yeung-Cheung said Hong Kong expatriates are ready to protest alongside them. There is talk of holding activities in conjunction with the July 1 demonstrations, which are held annually in Hong Kong to commemorate the city’s 1997 handover from Britain to China.

“For people overseas, what we want is for the next generation to have the life we used to have,” she said.

Cheung, the software engineer who went home to join the protests, agreed. Worried that his parents would disapprove of him flying home just to join the demonstrations, Cheung has been living with his brother. During the day, he tries distractedly to get work done; at night, he meets with high school friends to reminisce about “Old Hong Kong.”

As a boy, Cheung remembers, he looked up to the police officers in his neighborhood of Tung Chung. But on Friday, he joined thousands of demonstrators at the police headquarters in downtown Hong Kong to call for a formal investigation into their use of tear gas and rubber bullets days earlier.

Armed with goggles and a bottle of water, Cheung stood among his peers, chanting in Cantonese: “Shame on the Hong Kong police!”

Throughout the seven years he has spent in the United States, Cheung said, he always thought he would be returning home at some point. Now, he is not so sure.

“If Hong Kong is no longer Hong Kong, I don’t know what we’ll do,” he said.