Airborne transmission of Covid-19 amid poor ventilation could have led to 48 infections in a growing cluster at a K11 Musea restaurant, government adviser Yuen Kwok-yung says.
But it was an isolated incident and the mall should be safe.
Yuen is looking into the possibility of transmission via "infected tea" resulting from cross-contamination from utensils at Mr Ming's Chinese Dining at K11 Musea.
The Tsim Sha Tsui mall extended its closure to this Friday for staff and tenants to get a second test after compulsory testing was ordered for all staff and tenants on Saturday. By yesterday, 1,700 tests were conducted, with about 700 tests coming back negative.
Hong Kong reported 14 new cases yesterday - three imported and 11 local, including five from unknown sources - four of which were linked to Mr Ming's.
The cluster's tally hit 48, including 22 customers, nine staff and 17 close contacts, yesterday.
After an inspection yesterday, Yuen said Electrical and Mechanical Services Department officers found air changes on its ground floor to be just one third of the required threshold, while ventilation pipes were very narrow.
The Centre for Health Protection's controller, Ronald Lam Man-kin, said three of the infected diners at Mr Ming's went to Wong Chung Yan clinic in Tai Kok Tsui on February 22 and last Wednesday.
They were believed to have spread the infection to a nurse there, and more contact tracing found another patient to be preliminarily positive, after attending the clinic at the same time as the trio.
Lam said anyone who went to the clinic from February 22 will get mandatory test notices.
Three other patients had been to K11 Musea - two staff from Cartier and Twinkie Cookies, both on the ground floor, and a customer at Lilium on the fifth floor - and testef positive despite not having been to Mr Ming's.
Yuen said they could have contracted the virus outside the mall, as the inspection found ventilation and hygiene in other parts of the mall to be good. "Ventilation in the public area of the mall is fine. We went to the toilets for customers and staffers. They are also clean and come with good ventilation."
Meanwhile, social distancing measures, including the dine-in ban after 10pm, four-person gathering cap and compulsory mask wearing, were extended to March 17.