Microbiologist and government adviser Yuen Kwok-yung warned on Tuesday that "problems are bound to arise" as social distancing rules are being ignored as restrictions are being relaxed.
Speaking on a radio programme, the University of Hong Kong professor cited crowds at the Lan Kwai Fong area after the bars resumed operation.
The nightlife district was crowded over the weekend with people abandoning the government's social distancing rules, he said.
Yuen said that the government does not consult experts like him on everything, as they are only responsible for advising on scientific and medical principles for the government's policy making.
He said many activities can be resumed if there are targeted measures in high risk places, such as requiring people to keep their face mask on at all times while indoors and ensuring good ventilation.
The microbiologist also said he has written to the authorities to suggest that there should be minimal shared equipment in hospitals, such as blood pressure gauges to prevent cross contamination.