The protests, which came after a night of clashes with police, took place as demonstrators again made allegations of police brutality, reports the South China Morning Post newspaper.
Police published a Facebook post at about 11 a.m. on Thursday, warning that "guns have entered the community", and reiterated the threat firearms pose to human life.
"If anyone carries or uses genuine firearms in the city, this will pose a serious threat to public safety.
"If members of the public come across any pistol or rifle-like objects or suspicious articles, please leave immediately and make a report to the police when the situation allows," the post added.
Few hours later, dozens of black-clad activists in their masks marched inside Tai Po Mega Mall, chanting "Five demands, Not one less!" and "Disband the police".
They also called on passers-by to join a march planned for New Year's Day, organised by the Civil Human Rights Front.
The protests started peaceful, but clashes began when riot police were seen subduing several men outside the mall, said the South China Morning Post.
Black-clad and masked protesters also marched and chanted slogans in the Moko mall in Mong Kok on Thursday, with some holding a banner with the slogan "Free Hong Kong, revolution of our times".
Police said on Wednesday that 105 people had been arrested on Christmas Eve near the force's headquarters in Wan Chai, on suspicion of taking part in an illegal assembly.
( With inputs from IANS )