Rival groups of demonstrators clashed in Hong Kong and police made arrests in another weekend of mass protests after months of political unrest.

Dozens of pro-Beijing protesters waved Chinese flags and chanted “support the police” at a mall in Kowloon Bay on Saturday, as pro-democracy demonstrators gathered, clad in black and wearing masks. After a standoff, members of the two sides began to fight, throwing punches and hitting each other with umbrellas before police separated them. At least one man was seen bleeding from the head.

Groups of protesters shouted at each other and scuffled by a nearby “Lennon wall” – murals of protest art set up by demonstrators. Police were seen tackling and subduing several people, some of whom said they were local residents going to the mall.

'I'll take the blow for them': the volunteers protecting Hong Kong protesters Read more

As Hong Kong enters its fourth month of mass protests, tensions between supporters and critics of the pro-democracy movement have escalated. Earlier on Saturday, fights broke out between a group of pro-government demonstrators in blue T-shirts and residents in Fortress Hill after a Lennon wall had been torn down.

Videos showed groups of men using Chinese flags to beat mostly younger men. In one scene, a group chased and kicked a young man until a passerby shielded him with his body. Hong Kong’s hospital authority said 25 people were treated after Saturday’s clashes.

Hundreds of anti-government protesters in masks and all-black outfits were also marching in Tin Shui Wai, a neighbourhood in Hong Kong’s New Territories, defying a police ban on the planned event. Bus lines to the area were shut, as riot police faced off against protesters who blocked roads and built barricades on the streets, paralysing traffic.

Saturday marks the 15th consecutive weekend of mass protests in Hong Kong, where demonstrations against the government have deeply divided society. The protests, triggered by an extradition bill that would allow suspects to be sent to mainland China, has turned into a broader pro-democracy movement.

Hong Kong’s leader, Carrie Lam, has said that she will permanently withdraw the bill, but protesters have vowed to continue until all their demands are met. On Friday, thousands of protesters marked the mid-autumn festival by forming human chains across the city. Hundreds hiked to several peaks where they shined lanterns and torches.

Hundreds of secondary school students gathered in central Hong Kong, where they sang Glory to Hong Kong, a song that has become the unofficial anthem of the protests, and stuck signs and posted messages along a wall.

“I’m showing up to support the younger generation,” said Cheng, 21, a university student attending the rally of secondary students. “Just because one demand was fulfilled doesn’t mean we should back down. We should keep fighting for all five of the demands.”

He said: “There are a lot less people showing up to these kinds of protests and gathering, and I hope Hong Kong people will still remember what happened within these three months.”

During the past week, demonstrators have gathered in malls across the city to sing the anthem, in a departure from previous weeks of violent street battles with police.

Observers believe authorities are eager to stop the protests before 1 October, when China celebrates its national day, the 70th anniversary of the founding of the People’s Republic of China.

Many protesters believe it is a key date to apply more pressure on the government. One group has raised more than HK$8m (£820,000) to place adverts in the main newspapers on that day.

At a press conference given by protesters earlier in the day, demonstrators warned they would “escalate their ways” if the government continues to refuse their demands, which include an independent inquiry into police behaviour and democratic reforms to establish universal suffrage.

Protesters planned to come out again on Sunday, in defiance of a police ban on a march organised by the Civil Human Rights Front, an advocacy group that has organised several peaceful rallies in the past. Others planned to march on the British Consulate, to call on the UK to act on behalf of the former British colony.

Some worry that as school has started, the protests have lost momentum as fewer people have come out to the protests in the last few weeks. “Those who ever wavered might back down sadly,” said William, 29, a protester in Tin Shui Wai, who said he was disappointed with the number of people that turned out but would continue himself.

“I have to. I don’t want to miss out on history,” he said. “We have to keep it up. The revolution has started, and we must win.”