• Hong Kong police have arrested at least 300 protesters, as of around 8.30 p.m. on the first day China’s new national security law was enacted.
  • Protesters were faced with riot police, water cannon and pepper spray.
  • At least seven of the protesters were arrested for being in violation of the new law, the police tweeted. They were displaying pro-independence materials.
  • Visit Business Insider’s homepage for more stories.

Hong Kong police have arrested more than 300 people participating in protests, as of around 8.30 p.m., on the first day China’s sweeping new national security law came into force.

July 1 – the day the UK handed Hong Kong back to China in 1997 – is traditionally a day of protests, protected under the city’s Basic Law constitution.

But on Wednesday, when hundreds turned out in Causeway Bay, a busy shopping district, they were were faced by riot police.

Police kettled protesters, and used pepper spray and water cannon to disperse them.

According to the Hong Kong Police Force's official Twitter account, nine of the arrests were on suspicion of violating the new law, which forbids secession - any attempt at separating Hong Kong from mainland China.

One of these was a man with an independence flag, and another a woman holding a pro-independence sign, CNN reported.

Hong Kong Police also tweeted that "three females" were arrested for showing materials with pro-independence slogans. It is unclear if these are included in the earlier mentioned seven.

The penalty for secession can be between three and ten years and life imprisonment, according to South China Morning Post reporter Stuart Lau.

The other arrests were on suspicion of "offences like unlawful assemblies, disorderly conduct in public places [and] furious driving," according to Hong Kong police. An earlier tweet had also named "possession of offensive weapon" as one of the reasons for arrest.

The new law, which came into force late Tuesday night, is ostensibly intended to restore stability to Hong Kong, which has seen waves of protests since 2014.

However, it has been fiercely criticized for eroding the city's freedoms under the "one country, two systems" principle secured under the terms of its handover from the UK.

The full text of the new security law was made public only after it was passed.

It was drafted behind closed doors even without the input of Carrie Lam, Hong Kong's chief executive, CNN reported. Lam refused to offer comment on the law on Tuesday.

Details of the legislation have since been released. According to the document, the law imposes penalties on secession; subversion of the Chinese mainland's one-party rule; terrorism; and collusion with foreign forces.

However, the wording is vague, and experts have raised concerns about how broadly the law could be imposed.

Experts said the bill represents a blow to Hong Kong's autonomy, as Business Insider's Rosie Perper reported.

Its chilling effect was felt ahead of its passing as activist groups disbanded and hurried to erase social media posts.