A screenshot of the official Twitter page of Hong Kong Police Force confirms the first arrest made in Hong Kong by invoking provisions of the newly promulgated national security law.

HONG KONG - Hong Kong police on Wednesday arrested 10 people on suspicion of violating the newly promulgated national security law. 

In its official social media page, Hong Kong Police Force said the first arrest involved a man possessing a flag advocating Hong Kong independence in Causeway Bay on Hong Kong Island. Later, a woman carrying a placard advocating Hong Kong independence was arrested. 

A screenshot of the official Twitter page of Hong Kong Police Force confirms the second arrest made in Hong Kong by invoking provisions of the newly promulgated national security law.

Around 1.30 pm, some protestors at Causeway Bay started to occupy Hennessy Road, blocking multiple traffic lanes. Vehicles traveling along the lanes were forced to halt abruptly, according to a government press release. Given the huge crowds, some exits of Causeway Bay MTR station were temporarily closed.

A police officer was stabbed in the arm by rioters wielding sharp objects when he was making arrests. The suspects have fled and police strongly condemned such a violent act.

Three other police officers were injured when a motorcycle carrying a banner advocating "Hong Kong independence" rammed into them at full speed, police said in a social media post.

This photo from the official Facebook page of Hong Kong Police Force shows an injured officer in a blood-stained uniform after he was stabbed in the arm by protesters taking part in an illegal assembly in Causeway Bay, Hong Kong, July 1, 2020.

A police officer holds up a banner with a warning to protesters that their activities could result in arrests made by invoking provisions of the newly promulgated national security law. In Hong Kong's Causeway Bay on July 1, 2020. (PHOTO PROVIDED TO CHINA DAILY)

Police cited the law for the first time in confronting protesters Wednesday. “You are displaying flags or banners/chanting slogans/or conducting yourselves with intent such as secession or subversion, which may constitute offenses under the ... national security law,” police said in a message displayed on a purple banner.

Police fired water cannon to disperse the crowd and later said they had made more than 370 arrests for illegal assembly, obstruction, possession of weapons and for violating the new law as of 10 pm Wednesday.

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The law will punish crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison.

A screenshot of a photograph posted on the official Facebook page of Hong Kong Police Force captures material deemed offensive under the newly promulgated national security law.

Wednesday's arrest was the first since the Law of the People's Republic of China on Safeguarding National Security in the Hong Kong Special Administrative Region took effect at 11 pm on Tuesday.

The law was passed at the 20th session of the Standing Committee of the 13th National People's Congress, China's top legislature earlier in the day.