Prominent Hong Kong democracy activist Nathan Law has left the city for an undisclosed location, he revealed on his Facebook page.
He made the announcement shortly after testifying at a U.S. congressional hearing about the tough national security law China had imposed on the semi-autonomous territory.
In his post late Thursday, he said that he decided to take on the responsibility for advocating for Hong Kong internationally and had since left the city.
"As a global-facing activist, the choices I have are stark: to stay silent from now on, or to keep engaging in private diplomacy so I can warn the world of the threat of Chinese authoritarian expansion," he said. "I made the decision when I agreed to testify before the U.S. Congress."
Law told reporters in a WhatsApp message that he would not reveal his whereabouts and situation based on "risk assessment."
His departure comes days after Hong Kong's national security law took effect, targeting vaguely defined crimes of secessionist, subversive and terrorist acts, as well as any collusion with foreign forces in intervening in the city affairs.
"Under this legislation Beijing just passed about 24 hours ago, anyone who would dare to speak up would likely face imprisonment once Beijing targeted you," Law told the congressional hearing on Wednesday. "So much is now lost in the city I love: the freedom to tell the truth."
Law, 26, rose to prominence in Hong Kong as one of the student leaders of the pro-democracy Umbrella Revolution in 2014. In 2016, he became the youngest lawmaker elected to the city's legislature but was later disqualified for allegedly not taking the oath in a proper manner.
He was also part of pro-democracy group Demosisto, together with fellow activists Joshua Wong and Agnes Chow. All three resigned from the group Tuesday ahead of the national security law coming into effect. With the loss of its top members, Demosisto became dissolved.
The maximum punishment for serious offenses under legislation is life imprisonment, and suspects in certain cases may be sent to trial on the mainland if Beijing deems it has jurisdiction.
Critics say the law effectively ends the "one country, two systems" framework under which the city was promised a high degree of autonomy when it reverted from British to Chinese rule in 1997.
Hong Kong government on Tuesday night released a statement stating that popular protest slogan "Liberate Hong Kong, the revolution of our times" connotes a call for Hong Kong's independence or its separation from China, meaning those using it or displaying it on flags or signs could be in violation of the national security law.
On Wednesday, thousands took to the streets to protest the new legislation. Police arrested some 370 people, 10 of whom were detained on suspicion of violating the new law.
In some cases, suspects were found to be carrying paraphernalia advocating Hong Kong's independence, police said.
— ZEN SOO
Associated Press journalist Alice Fung contributed to this report.