Hong Kong recorded over 300 transmission chains for the second day - part of a fortnight's 1,921 confirmed cases that included 320 unknown-source infections.
There were 342 cases - all local - yesterday, while on Saturday the figure was 351, including eight imported.
Around 250 of yesterday's cases came from unknown sources. Another 300 preliminary positive cases awaited confirmation.
Most of the fresh cases with untraceable sources live or work in Sham Shui Po, Sha Tin, Yau Tsim Mong, Tuen Mun and Kowloon City.
Director of Health Ronald Lam Man-kin warned the rise of local cases is "unprecedented and will shock the city's anti-epidemic system."
Lam said the city, over the past two weeks, has seen over 320 untraceable infections and 80 percent of them involved the highly contagious Omicron variant.
"If one [untraceable] case represents one transmission chain, there are obviously over 320 transmission chains," Lam said.
"Bear in mind that one case can spread to more than one person. So, the minimum [ additional cases would be] over 320."
He warned the fifth wave has yet to peak. And it is not known when a "super-spreading event" that could spark a sudden exponential growth in infections would happen.
People should avoid social gatherings and the government should enhance testing and tracing to be prepared for a super-spreading event, Lam said.
The Centre for Health Protection's head of its communicable disease branch, Chuang Shuk-kwan, said three elderly care homes had infections yesterday, including the Ever Happy Aged Home in Sham Shui Po, where a 93-year-old unvaccinated woman tested positive.
More than 30 elderly residents and seven staff of the care home will be quarantined.
Chuang said a worker at Salvation Army Po Lam Residence for Senior Citizens tested positive and over 40 elderly have to be quarantined.
Another home, SAHK Lohas Garden in Quarry Hill, had two confirmed and two preliminary positive cases involving nurses and kitchen staff.
She said suspected vertical transmission was found at two residential buildings - Mei Shek House at Shek Mun Estate in Sha Tin and Hing Tai House at Tai Hing Estate in Tuen Mun.
Some virus carriers went to Po Lin Monastery on Lantau Island and Che Kung Temple during the Lunar New Year holiday, according to Chuang.
"We are worried transmissions could happen [at the temples] because Omicron could spread in crowded places even if people wore masks," she said.
The Hospital Authority's chief manager for quality and standards, Lau Ka-hin, said an 84-year-old unvaccinated man, infected with the Delta variant was sent to a hospital on Thursday but his condition deteriorated.
The man is at high risk of developing complications and death, which could have been reduced if he had been vaccinated, Lau said.
Three patients were detected at public hospitals, he added.
The patients included an 89-year-old woman at Kwong Wah Hospital, a 62-year-old woman at Queen Elizabeth Hospital and a 31-year-old man at Pok Oi Hospital.
Lau urged people whose testing results were positive should stay at home and follow the instructions of the Department of Health instead of rushing to public hospitals.
He stressed that going to emergency rooms will not speed up their admission process.
wallis.wang@singtaonewscorp.com
