The Hospital Authority says three nurses at Queen Elizabeth Hospital have tested preliminary positive for Covid-19, but the infections don't appear to be linked.
Two of the nurses worked together in an isolation ward and had taken care of coronavirus patients, with one of them also working on a medical ward. The third nurse also worked on a medical ward, but none of their patients are considered close contacts, since the nurses had worn full protective gear at work.
Nevertheless, all staff on the wards, as well as patients the nurses looked after, will be tested and the hospital will be thoroughly disinfected, officials said.
The Hospital Authority's general manager, Lau Ka-kin, told a daily press briefing on Monday that 10 members of staff who had meals with the nurses will be quarantined, and the medical wards they worked in will stop receiving new patients for the time being.
"Up to this moment, three medical wards are closed for admission of cases. So it would affect the admission of cases from the Accident and Emergency Department, if the patients need to be admitted to the medical ward," Lau said.
"We appeal to the Hong Kong citizens to try to avoid going to the Accident and Emergency Department of the Queen Elizabeth Hospital because of minor symptoms," he said, calling on people with mild illnesses to go to out-patient or private clinics instead.
Authorities reported 73 coronavirus cases on Monday - 69 of them local infections.
There were also more than 60 preliminary cases in total.
The Centre for Health Protection's Dr Chuang Shuk-kwan said 38 of the local confirmed cases did not have a clear source of infection.
Chuang said the proportion of unlinked cases is worrying as they could lead to an "exponential increase" in the number of new infections.
"I think there are still quite significant silent transmissions in the community. Not all cases are being picked up by our surveillance system," she warned.
"I urge the public if they have any mild symptoms, even they have undergone testing previously and have a negative result, they should go for testing and seek medical attention as soon as possible," said Chuang.
A top microbiologist, Yuen Kwok-yuen, who inspected Block Five of Laguna City in Yau Tong where there has been an outbreak, said only 400 or so of its residents, out of more than 700, had undergone mandatory tests.
Chuang said now that part of the building will be evacuated, all residents will be tested again. She said the government does not rule out law-enforcement action against those who flout the testing order.