The Hong Kong Special Administrative Region (HKSAR) government has called the massive Sunday protest – which had been granted approval earlier – "generally peaceful," emphasizing that no force will be used for an overall peaceful situation like this one.

"Yet police must make corresponding acts if any kind of illegal moves take place. That includes an appropriate level of force to curb violent acts," the government said in a statement, but also stressed that no illegal behaviors are permitted for the police officers.

Sunday's demonstration has appeared on course to be the biggest of its kind in recent months, with an estimated 183,000 participants, as the South China Morning Post quoted police as saying. It also marks six months since the protest initially broke out, sparked by the now-defunct fugitive bill that would have allowed suspects to be sent across the border to face trial. 

But there were still some radical protesters seen in the march, as police pointed out.

"In the evening, rioters spray-painted the exterior walls of the High Court; and threw petrol bombs outside the High Court and the Court of Final Appeal, damaging government property and seriously challenging the spirit of the rule of law," police wrote on their official Twitter account.

The authorities have classified the event as "arson" and pledged to investigate further.

Another group of violent protestors vandalized shops and a bank in Causeway Bay and the Wan Chai area. Officials have warned them not to commit any illegal acts that pose a threat to public order and endanger public safety. 

The public event, which was scheduled to start at Victoria Park and end in Central in Hong Kong, took place longer than expected, as some refused to leave when they arrived in Central. 

Some participants deviated from the approved route and occupied part of Gloucester Road and Des Voeux Road Central, said the police.

Ahead of the protest, police had found a semi-automatic pistol, 103 bullets among other weapons. According to Senior Superintendent Li Kwai-wah of Organized Crime and Triad Bureau, this was the first time a handgun has been seized. Eleven people were arrested in connection with the operation, police said in the statement.

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Hong Kong police seize pistol for first time during protests, arrest 11