Hong Kong police arrested about 400 people in New Year’s Day protests after what started as a peaceful pro-democracy march of tens of thousands spiralled into chaotic scenes with police firing tear gas to disperse the crowds.

The arrests take the total to about 7,000 since protests in the city escalated in June over a now-withdrawn bill that would have allowed extradition to mainland China, and will highlight the apparent absence of any progress towards ending the unrest.

The tension on Wednesday rose after some arrests were made in the Wan Chai bar district near a branch of global banking group HSBC, which has been the target of protester anger in recent weeks.

When scuffles broke out, large numbers of black-clad protesters rushed to the scene while other protesters formed human chains to pass them various supplies including bricks, forcing police to bring in their own reinforcements.

Police then asked organisers to call off the march early and crowds eventually dispersed as a water cannon truck and scores of police in riot gear patrolled the streets late into the evening.

Police said on Thursday they had arrested 420 people over the New Year holiday, most on New Year’s Day, with 287 of them in one sweep for illegal assembly, including a 12-year old. Police said they only made the arrests on Wednesday after they notified the march organisers and gave sufficient time for demonstrators to leave. Four officers were injured during the day, they said.