Hong Kong protesters set fire outside court buildings, threw petrol bombs and spray-painted graffiti on government buildings, marring what was otherwise a "generally peaceful" march over the weekend, police said on Monday.
The comments came as protesters called for strikes across the city on Monday. During the early morning rush hour most railway and transport links were running smoothly and there were no initial reports of widespread disruptions.
Vast crowds of black-clad demonstrators thronged the streets of the Asian financial hub on Sunday, in the largest anti-government rally since local elections last month and a resounding show of continued support for the pro-democracy movement.
While the march appeared to be largely peaceful - in marked contrast to other mass demonstrations over the last six months, where protesters fought pitched battles with police - authorities said there was some damage after it ended.
"Although the event was generally peaceful, acts of breaching public peace happened afterwards," police said in a statement on Monday.
"Some rioters spray-painted the exterior walls of the High Court, threw petrol bombs and set fire outside the High Court and the Court of Final Appeal, damaging government properties and seriously challenging the spirit of the rule of law," police said, adding that shops and banks were vandalized in the Causeway Bay and Wan Chai areas.
Protesters estimated the turnout at 800,000, while police said 183,000. In an editorial, the official China Daily newspaper called on the Hong Kong government to uphold the rule of law.
"Many residents in Hong Kong are fed up with the violence and disruption that have plagued the city for months. The record turnout for the district council elections showed they want to express their views peacefully," said the newspaper, often used by Beijing to put its message out to the world.
Hong Kong's new police commissioner had said he would take a "hard and soft approach" to the demonstrations, where acts of violence would be treated harshly but other issues more flexibly.
What started as demonstrations against a now-withdrawn bill allowing extradition to mainland China has morphed into calls for greater democratic freedoms and sometimes violent protests.
The former British colony has enjoyed relative calm in the weeks since the elections.
Protesters have set out five demands, including universal suffrage and an investigation into alleged police brutality.
On Saturday, two leaders of the American Chamber of Commerce in Hong Kong were denied entry to the neighboring Chinese city of Macau, without explanation.
China has repeatedly blamed foreign powers, including the United States, for stirring up the unrest.