Hong Kong police said Tuesday they have arrested six men in connection with a weekend attack at a subway station in which dozens of suspected gangsters beat up anti-government protesters and bystanders.

Senior Superintendent Chan Tin-chu said the men, aged between 24 and 54, are believed to have taken part in the violent attack at the rural Yuen Long MTR Station late Sunday.

They were arrested for "unlawful assembly" and some of them have connections to triad criminal gangs, he said, adding that the investigation is ongoing and more arrests could be made.

Local media reported that a seventh suspect has also been arrested, but the police have yet to confirm the arrest and what he was charged with.

Dozens of masked men wearing white T-shirts and armed with rods and sticks stormed the station around midnight Sunday, attacking people on platforms and in train compartments.

Reports quoted witnesses as saying that they appeared to target black-shirted protestors who had earlier attended a peaceful anti-government march in the city.

The hour-long incident saw the gang chasing and attacking people at random. Some victims suffered head injuries that left them bleeding. At least 45 people were injured.

The police were accused of colluding with the triad gangs by showing up late in response to calls for assistance and by letting the attackers go after they arrived at the scene in a bid to fence off the protesters to prevent them from protesting in Yuen Long.

Both government leader Carrie Lam and police chief Stephen Lo subsequently dismissed the allegations and said the police do not condone violence.

Earlier Sunday, hundreds of thousands of anti-government protesters took to the streets of central Hong Kong in an ongoing effort to push the government into totally withdrawing a now-suspended bill that would have allowed extraditions to mainland China.

After massing at the government complex, thousands of the demonstrators continued to march towards the Central Government Liaison Office, Beijing's representative office, to protest China's erosion of Hong Kong's freedoms, chanting "Revolt now! Reclaim Hong Kong!"

The office's plaque and the emblem of China were vandalized and anti-China graffiti were painted on the walls, leading to Chinese officials' condemnation of protesters who challenged Beijing's sovereignty over the territory.

"The protests were not about freedom of speech and freedom of assembly anymore," Chinese Foreign Ministry spokeswoman Hua Chunying told a press conference in Beijing on Tuesday.

She alleged there are signs that foreign authorities are "manipulating the situation, plotting, organizing or even executing the operation" and warned the United States against stirring up trouble in Hong Kong.

She was responding to a statement by the US State Department over the Yuen Long attack, in which it called the assault by gang members on citizens and journalists "disturbing" and expressed worries over the continued erosion of Hong Kong's autonomy.

On Monday, Andrew Murrison, British minister of state for international development, told the House of Commons that Britain was "shocked to see such unacceptable scenes of violence."