HONG KONG, March 14 (Xinhua) -- Some households in a residential building in Hong Kong's Tai Po area were evacuated to a quarantine center on Saturday night after three residents of the building were diagnosed with COVID-19, Hong Kong's Centre for Health Protection (CHP) said.

The CHP reported earlier Saturday three additional confirmed COVID-19 cases, one of them involves a 59-year-old male living in the same building with a couple who were members of a tour group to Egypt and were diagnosed with COVID-19 earlier this week.

An inter-departmental response team of the Hong Kong Special Administrative Region (HKSAR) government inspected the building on Saturday evening to identify the possible route of transmission.

Controller of the CHP Wong Ka-hing said at a media briefing after the inspection that the newly diagnosed patient lives in flat No. 13 on floor 34, the top floor of Heng Tai House of Fu Heng Estate, two floors above the couple. Out of prudence, the CHP decided to evacuate all the residents of flats No. 13 and No. 14 on the top six floors of the building to a quarantine center.

Yuen Kwok-yung, professor of the department of microbiology of the University of Hong Kong, said at the briefing that the epidemiological investigations are still ongoing and at the current stage the experts have not yet identified the route of transmission.

The evacuation decision was made as the experts assumed that the virus in the faeces of the couple might reach the rooftop through the exhaust vent and then carried down to the top few floors by the inter-building turbulence, Yuen explained.

The team have inspected the drainage pipes in the flats of the patients and found no problem that may lead to transmission. As for the remaining 28 floors of the building, engineers have examined the drainage pipes on 11 floors and are expected to complete the inspection of the remaining 17 floors on Saturday night, Wong said.

The CHP is proactively following up to see if any resident in the building is feeling discomfort, Wong said, adding that the CHP will collect the deep throat saliva specimens of the residents for tests on Sunday.