Two prominent Hong Kong opposition lawmakers were among more than a dozen people arrested Wednesday in a police operation focused on last year's huge protests, part of a widening crackdown against the city's democracy camp.

Lam Cheuk-ting and Ted Hui were detained after early morning raids on their homes, adding to the mounting prosecutions targeting Beijing's critics in the restless financial hub.

Both are minority Democratic Party lawmakers in the city's partially elected legislature and vocal critics of Beijing as well as Hong Kong's government and the police.

"This is out-and-out political persecution," James To, a veteran lawyer and fellow party member, told reporters.

Police said Wednesday's arrests were related to two anti-government rallies last year -- one on 6 July and the other on 21 July, the latter on a day that saw a notorious attack by government loyalists on protesters in the town of Yuen Long.

The brazen assault by more than 100 mostly white-clad men armed with wooden and metal poles helped fuel months of increasingly violent protests.

Police have charged eight people over the attack, some with links to "triad" organised-crime gangs.

Pro-democracy lawmaker Lam Cheuk-ting was detained in a raid early Wednesday morning
Pro-democracy lawmaker Lam Cheuk-ting was detained in a raid early Wednesday morning AFP / Anthony WALLACE

But they are now describing the clash as being between "evenly matched rivals".

"In today's operation, we arrested people who are believed to belong to the other side," senior superintendent Chan Tin-chu told reporters.

Lam, who was beaten bloody in the assault, was among 13 arrested Wednesday on suspicion of rioting, Chan said.

The group also included a senior bank official and a social worker, he added.

The Yuen Long attack, which was streamed live, was a defining moment of last year's pro-democracy protests.

Democracy supporters including Lam and Hui have accused police of deliberately arriving late to the scene, allowing the attackers to leave, and botching the subsequent investigation -- allegations the force has denied.

Beginning in early June last year, Hong Kong was hit by seven straight months of huge and often violent pro-democracy protests
Beginning in early June last year, Hong Kong was hit by seven straight months of huge and often violent pro-democracy protests AFP / DALE DE LA REY

Pro-Beijing figures hailed the latest police action.

"Justice may be late but never absent," said lawmaker Junius Ho, who was seen shaking hands with some of the white-clad men in Yuen Long before the attack.

Lo has denied prior knowledge of the assault and said he was simply greeting patriotic locals. On Wednesday he said he has "clean hands that need no washing".

Antony Dapiran, a Hong Kong lawyer who has written books about the city's protests, described the police recasting of the Yuen long attack as "gaslighting of the highest order".

"HK govt and police (are) trying to rewrite the narrative of one of the most documented and live-streamed events of last year," he wrote on Twitter.

Beginning in early June 2019, Hong Kong was hit by seven straight months of huge and often violent pro-democracy protests in which more than 9,000 people were arrested.

The unrest upended the city's reputation for stability and sparked a crackdown by China that has gathered pace this year.

In late June Beijing imposed a sweeping new security law, tightening Communist Party control over the semi-autonomous city and ending the legal firewall between the two territories.

Certain political views -- such as advocating independence or greater autonomy for Hong Kong -- became illegal overnight, and arrests have followed.

In response to the law, many Western nations ended extradition agreements with Hong Kong.

The United States has placed sanctions on some Chinese and Hong Kong officials and declared the business hub no longer sufficiently autonomous from the authoritarian mainland.

The democracy protests died down at the start of 2020 thanks to the mass arrests and coronavirus restrictions.

City leader Carrie Lam began the year vowing to heal divisions.

But police have since arrested dozens of prominent pro-democracy figures on a slew of charges related to the rallies, with the courts now filled with hearings and trials.