Caspar Tsui was among 15 officials who went to the 53rd birthday of Witman Hung, a city delegate to the national legislature, before new COVID-19 restrictions came into force, but after Hong Kong leader Carrie Lam appealed to people to avoid big gatherings.

Tsui "brought the Hong Kong government into disrepute" and "did not meet the expectations of the general public", Lam told a news conference.

"I accepted his resignation," she said.

Hong Kong has followed China with a zero-COVID policy despite the economic costs and a rising psychological toll on many people of the tough restrictions aimed at keeping the virus at bay.

Tsui said in a statement he had made a wrong decision to attend the banquet on Jan. 3 when all efforts should have been devoted to controlling the spread of the virus.

"As one of the principal officials taking the lead in the anti-epidemic fight, I have not set the best example," Tsui said.

Lam, announcing the results of a city government investigation into the party, said 12 of the government officials who attended had been cleared.

Two, Allen Fung, a political assistant to the secretary for development, and Vincent Fung, an official in the Policy Innovation and Co-ordination Office, would be issued verbal warnings, she said.

Lam said the 12 officials who would not be sanctioned had only attended the party briefly.

Among them were Director of Immigration Au Ka-wang, police commissioner Raymond Siu and the head of the city's Independent Commission against Corruption, Simon Peh.

All government officials involved have issued public apologies.

It was the second run-in with COVID regulations for Au.

Last year, he paid a fine for attending a dinner at a luxury private club with more people than the four allowed to gather.

About 20 members of Hong Kong's new "patriots-only" legislature also attended the party. All government officials and legislators have repeatedly tested negative.