HONG KONG, China - Hong Kong's first "patriots only" district council elections saw a turnout of 27.5 percent, the government said Monday, a record-low number for a race that had shut out all opposition candidates.

The city last held district council elections at the peak of huge, sometimes violent, democracy protests in 2019, recording a historic-high 71 percent turnout that delivered a landslide victory for the democracy camp.

But a clampdown on dissent -- aided by a sweeping national security law imposed by Beijing -- has included a drive by authorities to weed out from public office anyone deemed politically disloyal after the protests.

Sunday's voting day stretched to midnight, after a rare 90-minute extension was granted following a failure in the digital system used to confirm voters' eligibility.

Despite the extra time, the government's official website was updated on Monday morning to show a final turnout of 27.54 percent, with just shy of 1.2 million out of 4.3 million registered electors having gone to the polls.

Previously, the lowest turnout rate since the city's handover to China was 35.82 percent, recorded in 1999.

City leader John Lee had thanked the "more than 1 million" voters at around 1:45 am Monday (1745 GMT Sunday) for coming out.

After voting Sunday, he said this year's election was "the last piece of the puzzle to implement the principle of patriots ruling Hong Kong".

"From now on, the district councils would no longer be what they were in the past -- which was a platform to destruct and reject the government's administration, to promote Hong Kong independence and to endanger national security," Lee said after he cast his ballot on Sunday.

According to new rules announced in May, the number of seats that could be directly elected was slashed from 462 to 88, with the other 382 seats controlled by the city leader, government loyalists and rural landlords.

Candidates were also required to seek nominations from three government-appointed committees, which effectively shut out all pro-democracy parties.

Over 70 percent of the candidates picked to run for the election were themselves members of the nominating committees.

Police also acted swiftly to clamp down on any sign of dissent on Sunday, arresting at least six people.

Three were activists from the League of Social Democrats -- one of the city's last remaining opposition groups -- which had planned to stage a protest.

Police first accused the trio of "attempting to incite others to disrupt district council elections" and later passed them to the Independent Commission Against Corruption (ICAC) over suspicion of "inciting others not to vote".

The League called the arrest "extremely ironic and ridiculous".

On Friday, the national security police arrested a 77-year-old man for an "attempt to carry out seditious acts".

A 38-year-old man was charged on Tuesday for reposting a video of an overseas commentator that allegedly incited people to boycott the election.