Most of the officials who were there maintained that they had only dropped in briefly to greet birthday boy Hung, leaving some observers to say it was unlikely that civil service protocols were breached.

Late on Friday, city leader Carrie Lam Cheng Yuet-ngor announced an investigation into the 13 officials who attended.

They included Director of Immigration Au Ka-wang, home affairs chief Caspar Tsui Ying-wai, Police Commissioner Raymond Siu Chak-yee and Independent Commission Against Corruption (ICAC) chief Simon Peh Yun-lu.

Lam said in a statement that the probe would be headed by director of the Chief Executive’s Office Eric Chan Kwok-ki and Secretary for the Civil Service Patrick Nip Tak-kuen.

She added that the officials would have to use their own personal leave to cover their quarantine stay, and their deputies would take over in their absence.

Political scientist Ma Ngok, from Chinese University, asked: “Why were so many law enforcement people there, especially the head of ICAC?”

Lawmaker Regina Ip Lau Suk-yee, who did not attend the party, also questioned why officials were at Hung’s party.

“Why the need to socialise so much? They might as well stay home and read more documents and conduct more policy research,” she said on a radio show on Friday.

Home affairs chief Tsui faced the most intense censure by the city leader for being the official who stayed the longest.

Pressure is also mounting on law enforcement agencies to open criminal investigations into what took place at the party.

On Friday, the Food and Environmental Hygiene Department announced a probe on the restaurant and its guests.

Two legal experts, including Executive Council member and senior counsel Ronny Tong Ka-wah, believe that social-distancing laws may have been broken.

Tong and barrister Albert Luk Wai-hung pointed to the guests’ failure to wear masks at the restaurant and whether the number of guests exceeded the legal limit.

In one photo, birthday boy Hung is seen singing without a mask, with other guests also unmasked and chatting.

Current rules require restaurant patrons to be masked except when eating or drinking. Tong said there was a legal liability on both the restaurant operator and patrons to obey the rule.

Luk said a second possible offence was some guests’ failure to use the “Leave Home Safe” risk exposure app when entering the restaurant. Under current rules, failure to use the app amounts to an offence.

A third possible offence, both Tong and Luk pointed out, was the crowd size.

“With many people coming and going, the number of guests could well have exceeded the legal limit and mixing of patrons across tables seems to have happened,” Luk said.

All the three offences carry penalties ranging from a fine of HK$5,000 (US$641) to up to a jail term of six months.

Replying to a query from the Post on Friday, police said they would “take corresponding actions on the basis of actual circumstances and according to the Prevention and Control of Disease Ordinance”.

Anger, apologies as top Hong Kong officials caught in Covid-19 party scandal

Andy Ho On-tat, who served as former chief executive Donald Tsang Yam-kuen’s information coordinator, highlighted the need for fact-finding in deciding which officials at the party should be held responsible.

But Luk said a criminal probe was necessary to restore residents’ trust in the public health rules.

“The public is outraged and crying out for answers. A police probe can provide answers even if in the end, the legal advice obtained is not to take the matter to court.”

Additional reporting by Gary Cheung