Gabriel Leung Cheuk-wai, also a government adviser on the pandemic, said he is “not optimistic” about the city’s pandemic situation, after sewage samples of multiple residential buildings in Sai Ying Pun and Mid-Levels returned positive with the virus.

His remarks came a day after a ballooning outbreak at Ursus Fitness in Sai Ying Pun added 47 more cases, taking the number of infected staffers, customers and close contacts to 64, among which were students from international schools, and white-collar employees at banks and law firms.

Speaking after a radio program, Leung added health authorities also saw the same results in screenings of sewage in Central and Sheung Wan buildings, but health authorities failed to trace patients linked to the area, meaning there are still hidden carriers in the community.

He noted there was a rapid spreading from the gym cluster, as health officials reported second and third-generation infection cases just within three days.

"I think we're at an extremely critical stage where we may be at an inflection point between the nadir that we have seen to have finally achieved to bring the fourth wave under control, with about a week's worth of single-digit new cases," Leung told reporters.

"And I think it all rather depends on the extent and the intensity of our mitigation effort to detect, monitor and pick out all of the potentially infected cases arising from this superspreading gym cluster."

Leung urged visitors of fitness centers, offices or residential buildings with confirmed cases to get tested as soon as possible and refrain from non-essential social activities.