Government pandemic advisor David Hui on Saturday said members of the public should not buy oral Covid drugs on the black market, as a prescription was needed to ensure safety.

"It is not advisable to go to the black market to purchase unregistered drugs because you don't know whether there will be drug interaction," he said, citing scenarios when doctors have to prescribe specific Covid drugs to patients taking other medicine.

Speaking after attending a radio programme, the Chinese University respiratory medicine professor said for example the registered antiviral Paxlovid, which is made by the US drug company Pfizer and is used here legally to treat many Covid patients, was not suitable for a person taking anticoagulants or antiarrhythmics.

So far this month, Customs have made two large seizures of unregistered oral Covid drugs with officers on Friday announcing 2,100 boxes had been confiscated at the airport. It followed a bust last week at the airport and at a Tin Shui Wai flat.

With regard to public hygiene, Professor Hui said Hong Kong should follow the example of some other Asian countries and mandate mask wearing in certain situations, even if the general mask wearing mandate were to be cancelled following the winter flu season.

"There are some scenarios in which we need to continue universal masking - including travelling by public transport, going to healthcare facilities like hospitals and clinics, and in the nursing home and disabled home settings. Because these are the high-risk areas," Hui said, citing similar measures in Singapore and South Korea.

His comment comes two days after health authorities announced that from January 30 people with Covid will no longer have to isolate or report their infections to health authorities.