Hong Kong police have arrested more than 2,000 people in raids on suspected criminal triad gangs, with the city's underworld in the spotlight after a lawmaker received death threats.

The raids, which started in late July, have netted 2,120 people believed to be connected with triad, vice and dangerous drugs offences, Hong Kong's organised crime chief told reporters.

The operation, named Thunderbolt 16, also seized HK$62 million ($8 million) worth of drugs including heroin, cocaine and ketamine.

The announcement comes a day after police said separately that six men believed to have triad links had been arrested in connection with threats to newly elected city lawmaker Eddie Chu.

Chu has taken on pro-establishment rural strongmen accused of having criminal links and colluding with the government and business figures for their own benefit.

The 38-year-old lawmaker is also calling for more autonomy from China for Hong Kong.

Chu says he and his family have not been able to return home since elections on September 4 because of death threats.

Acting senior superintendent of crime Li Kwai-wah said Thursday the six men arrested in Chu's case had been detained for "criminal intimidation" linked to his allegation that he had been followed on election day.

Chu's accusations have renewed speculation over triad links to Hong Kong politics.

Triad gangs have traditionally been involved in drug-running, prostitution and extortion but increasingly operate in legitimate ventures such as property and the finance industry.

Some are believed to have links with the political establishment and there have previously been claims of triads sending paid thugs to stir up trouble during protests.