HONG KONG: Two prominent Hong Kong opposition lawmakers were among more than a dozen people arrested on 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 toll of prosecutions targeting Beijing's critics in the restless financial hub.

Both are minority pro-democracy 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 member of their Democratic Party, 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 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 sent already swirling distrust of authorities skyrocketing and helped fuel further months of increasingly violent protests.

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

Police 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 on suspicion of rioting, Chan said.

The group also included a "vice president of a bank" and a social worker, he added.

The Yuen Long attack was a defining moment of last year's pro-democracy protesters.

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

Pro-Beijing figures hailed the latest police action.

"Justice may be late but never absent," lawmaker Junius Ho told reporters.

Ho was seen shaking hands with some of the white-clad men in Yuen Long before the attack.

He has denied having 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".

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 popular 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 mass arrests and anti-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.