A top microbiologist said on Wednesday that he expects between 1 to 5 percent of the more than 500 Hong Kong residents being evacuated from Hubei to be infected with Covid-19.

Ho Pak-Leung, who heads the University of Hong Kong's Centre for Infection, said these cases may involve people who have been infected, but have not yet developed symptoms.

Ho also said it was the stepped-up vigilance of the Hong Kong people which had prevented widespread outbreaks like in Italy and Iran, as the SAR had seen the first positive case back in January.

He noted that almost 95 percent of the people in Hong Kong started wearing masks as a precaution after that.

He said this prevented large scale flare-ups despite the crowded environment and dense housing in Hong Kong.

The expert said government measures to prevent outbreaks were good, but the implementation was slow and had some loopholes.

He pointed out that people travelling from the mainland can still enter Hong Kong if they come via Macau as the government has not prescribed quarantine for people coming in from the neighbouring SAR.