Hundreds of pro-Beijing demonstrators sang the Chinese national anthem, waved red flags and chanted slogans at Amoy Plaza in the densely packed Kowloon district.
Skirmishes broke out Saturday between supporters of the ongoing protests for democratic reforms in Hong Kong and supporters of the central government at a shopping mall in the semi-autonomous Chinese territory.
Hundreds of pro-Beijing demonstrators sang the Chinese national anthem, waved red flags and chanted slogans at Amoy Plaza in the densely packed Kowloon district. Counter-protesters quickly gathered there, sparking tensions as the two camps heckled each other.
The situation turned chaotic, with groups of people trading blows and some using umbrellas to hit their opponents.
Police later moved in to defuse the situation, with several people detained.
The clashes amid the mid-autumn festival holiday came after several nights of peaceful rallies that featured mass singing at shopping malls by supporters of the months-long pro-democracy protests.
Thousands of people also carried lanterns with pro-democracy messages in public areas and formed illuminated human chains on two of the city's peaks on Friday night to mark the major Chinese festival.
Caroline Malone reports from Hong Kong.
Protesters have refused to yield despite the government's promise to withdraw an extradition bill that triggered the protests.
They have widened their demands to include direct elections for their leaders and police accountability.
Many saw the extradition bill, which would have allowed some Hong Kong suspects to be sent to mainland China for trial, as an example of Hong Kong's autonomy eroding since the former British colony returned to Chinese rule in 1997.
Shops shuttered at Amoy Plaza after the brawls. The atmosphere remained tense as pro-democracy protesters slammed police, some who were seen hitting detainees with batons to subdue them. Local media showed minor scuffles continuing outside the mall as people left.
In the northwestern suburb of Tin Shui Wai, several hundred people marched on the street, carrying pro-democracy posters and waving American flags, in defiance against a police ban on a rally in the area.
More than 1,300 people have been arrested since the protests began in early June. The unrest has further battered Hong Kong's economy, which was already reeling from the US-China trade war.