Long queues formed down streets, in residential estates and at businesses-turned-polling stations, with people casting an online ballot on their mobile phones after having their identities verified.
Hong Kong police on Friday raided the office of election co-organiser Public Opinion Research Institute (PORI), the night before the democratic primaries, local broadcaster HK01 reported.
Defying warnings from a senior Hong Kong official that the vote might fall foul of the national security law, residents young and old flocked to more than 250 polling stations across the city, manned by thousands of volunteers. Organizers denounced the move as an attempt to disrupt the vote or intimidate people, while police said it was linked to a tip on possible pirated data.
The police raid may have assisted in assisting to publicize the primary election, however, with the news of the event circulated throughout the city.
"I did wonder whether it would be the last time I took part in such a primary", Kitty Yau told the paper. "But I am not scared of any "white terror" as I am just training my rights".
There has been a marked chill on city policy since the passage of the security law, which was imposed directly by Beijing, bypassing the Hong Kong legislature.
In the hours after it became law, multiple political parties disbanded, including one founded by prominent activist Joshua Wong. Shops and restaurants that had been vocal supporters of the anti-government protest movement could be seen hastily removing posters, for fear of being prosecuted under the new law.
"Now is the second week after the implementation of national security law".
Hong Kong and mainland Chinese officials have defended the law as a necessary step to curb months of sometimes-violent unrest that rocked the former British colony previous year before the global Covid-19 pandemic quieted the city's protest movement. Canberra said it would also offer a citizenship tour for Hong Kongers, following the UK's promise to allow the 3 million Hong Kongers to settle down.
The Amcham survey, published on Monday and to which 183 or 15% of its members responded on July 6-9, showed 36.6% of respondents were "somewhat" concerned and 51% were "extremely concerned" about the legislation.
"The uncertainty of the rules is a little stressing and the present conflict concerning USA and China", 1 respondent was quoted as expressing. "This may lead to a situation where China arrests people based on political motives".
Some 68% of respondents stated they experienced turn out to be more concerned about the law as aspects have emerged, with a single respondent declaring "vague language would make the law a great device for rule by legislation, and is by now major to the variety of self-censorship that is so productive at stifling community discourse in China".
When asked what concerned them most about the law, companies largely echoed concerns voiced by foreign governments and civil society groups, saying they are anxious about the ambiguity of the legislation's scope and enforcement, the threat it poses to Hong Kong's prized independent judicial system and the risk the city could lose its status as a global financial hub.
CNN's Eric Cheung contributed reporting.