Organizers of what was once an annual commemoration of China’s 1989 crackdown on pro-democracy protesters face up to 10 years in prison under the Beijing-imposed law.

A vigil at Hong Kong`s Victoria Park on June 4, 2019, commemorating the 30th anniversary of the Tiananmen Square crackdown.Anthony Kwan / Getty Images

Hong Kong`s High Court on Thursday began hearing the landmark national security trial of three former leaders of a now disbanded group that organized annual vigils marking Beijing`s 1989 Tiananmen Square crackdown on pro-democracy protesters.

Once legal in China-ruled Hong Kong, such public commemorations were hailed as a symbol of the city`s relative freedom compared with mainland China.

The events on June 4, 1989, when Chinese troops opened fire to end student-led protests, are not publicly discussed in China, which treats the date as taboo and allows no public remembrance.

Dozens of people lined up overnight outside the West Kowloon Magistrates` Courts building despite a cold weather warning, with scores of police officers and vehicles deployed amid tight security.

Tang Ngok-kwan, a former senior member of the disbanded group, the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, said he lined up for several days to get in the courtroom out of respect for the trio`s sacrifices.

"Justice resides in the hearts of the people, and history will bear witness," he said.

Blocked in 2020 over Covid-19 curbs, the commemorations have never resumed since China imposed a tough national security law that year. Several June 4 monuments, such as the "pillar of shame," have also been removed from three local universities.

Under the national security law, Lee Cheuk-yan, 68, Albert Ho, 74, and Chow Hang-tung, 40, the three former leaders of the now-disbanded group, face charges of "inciting subversion of state power" that carry punishments of up to 10 years in jail.

The trial is among the last of several such major cases, with Chow, the former vice chair of the group, held on remand for more than 1,500 days after being denied bail.

Activist Lee Cheuk-yan, wearing a mask, after a court hearing in Hong Kong in 2020.Isaac Wong / SOPA Images/LightRocket via Gett

In an opening statement, prosecutors said the case centered on whether the Alliance`s publicly stated goal of "ending one?party rule" constituted illegally inciting others to carry out acts aimed at subverting state power.

The other key focus of the case is whether such acts amounted to "overthrowing or undermining" China`s system of government, they added.

Rights groups and some foreign governments have criticized such national security cases against prominent democrats as a weaponization of the rule of law to silence dissent.