Hong Kong police on Monday urged the city's residents to demonstrate peacefully and to shun violence during a planned New Year's Day rally — after a letter not objecting to the event was issued a day earlier.

The police made the comments during a news briefing on Monday as they strongly condemned renewed violence over the past weekend when some demonstrators adopted very aggressive tactics. Such behavior could not be condoned, the police public relations chief said.

After one-month-long lull, violence and vandalism returned on Christmas Eve as rioters smashed and looted shops, banks and restaurants. Black-clad protesters set fire to Mong Kok MTR station and greatly disrupted several major shopping centers, including Landmark North in Sheung Shui and Telford Plaza in Kowloon Bay.

During an arrest made in Sheung Shui on Saturday night, one rioter resisted and grabbed a firearm from police officers. He later even put his finger on the weapon's trigger which posed a threat to public security, explained Kenneth Kwok Ka-chuen, chief superintendent of the Police Public Relations Branch.

The violence during the two-day Christmas holidays were "no doubt" criminal acts, aimed at causing chaos and disrupting the social order, explained Kwok. He added that the vandalism over the weekend had sounded an alarm about future protests. He cautioned against possible violence during the New Year's rally organized by the Civil Human Rights Front.

The CHRF has estimated over 300,000 people will participate in the New Year's Day march. The front had estimated a turnout of around 800,000 for its last anti-government march on Dec 8, while police put the peak figure at only 183,000.

Kwok urged Hong Kong citizens to avoid any violence during the incoming rally, and also hoped the public could stop covering up or glorifying aggressive acts.

The chief superintendent appealed to the organizer and participants to demonstrate in a peaceful and orderly way. He said police would act quickly and take any actions necessary to protect people and their property if the New Year's march became violent.

Meanwhile, during the briefing, police said they were "very concerned" about a trend that a rising number of young people have been incited to commit violent crimes. According to police, 34 people were arrested over the Christmas weekend; the youngest was only 13.

"All these worrying facts indicate a weaker law-abiding awareness among young people," the chief superintendent said. He called for joint efforts by social organizations to assist young people who had been arrested.

Kwok also warned people with ulterior motives not to take advantage of young students who were often not mature enough to tell right and wrong.