BBC reports that Hong Kong police are facing accusations of failing to protect pro-democracy activists who were attacked by unidentified assailants on Sunday.
Opposition lawmakers say police inaction allowed criminals to beat up peaceful demonstrators after a rally.
Dozens were injured when they were set upon by masked men wielding sticks.
Police say their forces were stretched during another day of unrest. Hong Kong has been rocked by weeks of protests sparked by an extradition bill.
Late on Sunday video footage showed groups of men – dressed in white shirts and suspected to be triad gangsters – beating passengers with rods at a train station in the Yuen Long area.
There is speculation that the attackers have links with criminal gangs, known as triads. Forty-five people were injured, with one person in critical condition.
Hong Kong’s Chief Executive Carrie Lam described the attacks as “shocking”. She also condemned protesters for defacing China’s main representative office in the city earlier in the day.
One of the pro-democracy lawmakers injured in the attack, Lam Cheuk-ting, criticised the police response and suggested the assailants were linked to gangs.
“Is Hong Kong now allowing triads to do what they want, beating up people on the street with weapons?” he told reporters.
Another pro-democracy legislator, Ray Chan, tweeted: “Hong Kong has 1 of the world’s highest cop to population ratio. Where were @hkpoliceforce?”
Alvin Yeung, who leads the Civic Party, said: “This is triad gangs beating up Hong Kong people. Yet you pretend nothing had happened?”
Hong Kong police chief Stephen Lo defended his forces, saying his officers were busy dealing with violent anti-government protests elsewhere.
“Our manpower is stretched,” he said. Mr Lo called suggestions that police had colluded with triads a “smear”, adding his officers would pursue the attackers.
No arrests have been made so far.