Hong Kong’s opposition Democratic Party is investigating attacks by suspected triad gangsters on train passengers on Sunday, after a night of violence opened new fronts in the political crisis now deepening across city.

Screams rang out when men, clad in white t-shirts and some armed with poles, flooded into the rural Yuen Long station and stormed a train, attacking passengers, according to footage taken by commuters and Democratic Party lawmaker Lam Cheuk-ting.

Some passengers had been at an earlier anti-government march and the attack came after several thousand activists surrounded China’s representative office in the city, later clashing with police.

Lam, who was injured in the attack, said he was angry about a slow police response after he alerted them to the trouble, government-funded broadcaster RTHK reported.

Lam said the police action had failed to protect the public, allowing the triads to run rampant. The party is now investigating.

“Is Hong Kong now allowing triads to do what they want, beating up people on the street with weapons?,” he asked reporters.

Hong Kong has been rocked by a series of sometimes violent protests for more than two months. Protesters are demanding the full withdrawal of a bill to allow people to be extradited to mainland China for trial, where the courts are controlled by the Communist Party, and independent inquiries into the use of police force against protesters.