Officers said the weapons, which included box cutters, razor blades and scissors, were taken from 358 protesters who were detained and searched near the old Wan Chai police station on Gloucester Road.

Police said other items found on the protesters included cable ties and incriminating shirts, masks and goggles.

Lee Kwai-wah, the senior superintendent of the Organised Crime and Triad Bureau, said the confiscated items indicated the confrontation with police was planned.

“They were organised and prepared radical individuals. The masks and shirts were used to hide their identities. Cable ties were used to bundle the metal barriers,” Lee said.

“What we were worried the most about were the weapons, including the scissors and razors, which posed great threats to officers and to protesters themselves.”

Officers arrested 12 of the protesters for unlawful assembly. Another 358 demonstrators were found weapons and other items, but were released after police searched them and recorded their personal information.

Lee said there were 265 men and 93 females. He said 81 per cent of the briefly detained protesters were younger than 25. The youngest was 16, and 24 of the protesters were younger than 18.

Lee said all of the protesters who were held could face arrest in the future on charges of unlawful assembly. He did not provide any other details about the protesters, but said that officers were investigating.

“I cannot disclose if these people are from any political party because that is part of our investigation,” Lee said. “But regardless, they were involved in very violent acts.”

Kong Wing-cheung, the senior superintendent of the Police Public Relations Branch, said seven men were arrested for unlawful assembly in the area of the clashes.

He brushed aside rumours that police had used tear gas to fight off the protesters, saying officers only used pepper spray and batons.

The bill would allow the transfer of fugitives to jurisdictions with which Hong Kong has no extradition agreement, including mainland China.

As the main rally started to wind down at about 10pm, hundreds of protesters started to gather around the Legislative Council. At around midnight, hundreds of masked protesters raced towards the police lines and tried to force their way into the legislature.

Protesters used bottles and metal barricades to attack the police, who responded with batons and pepper spray. Some protesters were wrestled to the ground and taken away.

Kong did not respond to questions on whether the police made a mistake and gave the protesters a chance to storm the legislature, and later gave them a chance to occupy Gloucester Road.

He said only that the force had conducted its risk assessment protocol and deployed officers based on the situation.

Kong also refused to discuss whether police would provide tighter security blanket around the Legco after some groups threatened to besiege the building during the second reading of the bill on Wednesday.