A man was arrested for holding a Hong Kong independence flag, the police force wrote on Twitter, adding that it was a violation of the new law passed by Beijing, which was implemented on Tuesday night.

“This is the first arrest made since the law has come into force,” Hong Kong police tweeted.

The force announced on Monday that they would deploy between 3,000 and 5,000 officers in light of potential unrest on Wednesday, as protests were planned to mark the 23rd anniversary of Hong Kong’s handover from Britain to China.

Civil Human Rights Front, the group that organized the city’s largest protest marches over the last year, had vowed to go ahead with a banned march despite having no permit.

The national security law targets secession, subversion, terrorism and collusion with foreign forces in Hong Kong. Critics say its purpose is to quash dissent in the financial hub, which has been roiled by protests for the past year.

Under the new law, “serious offenders” may face life imprisonment, or a fixed term of no less than 10 years.

Those engaged in minor actions – such as flag waving, slogan chanting or displaying banners – could face punishment of between three and 10 years in prison.

The law was gazetted into an annex of Hong Kong’s Basic Law late Tuesday after it was given the go-ahead at the end of a three-day deliberation by the National People’s Congress Standing Committee, who voted unanimously to push the law ahead.

There are fears the law will undermine the autonomy promised to Hong Kong under the “One Country, Two Systems” principle agreed by China and Britain to guarantee certain freedoms for the territory until 2047. (dpa/NAN)