The Hong Kong government has tightened social distancing measures as clusters continue to emerge, leading health experts to warn of a new wave of Covid-19.

At the daily briefing yesterday, Secretary for Food and Health Bureau Sophia Chan said there had been an additional 42 confirmed cases, of which 34 were the result of local transmissions.

Of the local coronavirus cases, 23 were linked to an elderly care centre located in Tsz Wan Shan and the rest were connected to taxi drivers and eateries.

The authorities could not trace the source of two local infections.

The additional cases bring the total confirmed tally of patients to 1,365, including seven deaths.

Given the community spread, Professor Chan said that for 14 days, starting from tomorrow, the operating capacity of all eateries will be capped at 60 per cent, down from 100 per cent now. No more than eight patrons will be allowed at one table, while in bars and pubs that number will be capped at four. Small eateries must put up partitions on tables for patrons.

The maximum number allowed at venues where people can remove their face masks, such as karaoke lounge rooms, party rooms and gyms, has also been halved from 16 to eight, while cinemas will again not serve food and drinks. Nightclubs can only run at 60 per cent capacity, with the maximum number of customers per table halved from eight to four.

From today, geriatric and psychiatric services at public hospitals will be suspended.

"Now is the time for us to suppress and the focus of this suppression is really on mask-off activities. We understand from the recent clusters and also the confirmed cases that a number of them are from the catering business (cha chaan tengs or cafes)," Prof Chan said, adding that the authorities are increasing checks in these areas.

She also said the government will step up voluntary testing of staff at nursing homes and eateries, as well as public transport drivers.

Besides expanding the areas to be tested, the government has also been ramping up testing capacity.

Over March and April, the government conducted over 66,000 tests and this rose to 75,000 in May and more than 100,000 last month.

The announcement on the tightening of measures came just hours after infectious disease expert Ho Pak Leung from the University of Hong Kong called on the government to act promptly as the Covid-19 situation appeared to be returning to what it was in March, the height of the second wave of infections.

He was quoted by RTHK as saying that there was a good chance the recent spike was caused by loopholes in the system like quarantine exemptions for some groups.

He also urged people to order takeaways instead of dining out as well as to disinfect seat belts and buckles when getting into a taxi and to lower the windows of the vehicle on both sides to allow air to circulate.

The latest cases are in addition to the 24 confirmed on Wednesday, of which 19 were local. The rest were imported.

Health officials had expressed fears of a wide community outbreak after cases emerged in different areas of the city, including on Hong Kong Island, in Mong Kok and Tsuen Wan.

About half of the new local cases reported on Wednesday were linked to the elderly care home in Tsz Wan Shan.

The remaining ones were linked to restaurants in Choi Hung and Jordan.

The spike in cases comes after three weeks when the numbers were tapering off.

Meanwhile, United Airlines has extended its suspension of flights to and from Hong Kong in the light of new testing protocols for crew arriving in the Asian financial hub.

American Airlines also cancelled its plans to resume services from Dallas/Fort Worth.

Hong Kong updated its Covid-19 prevention and control measures this week, requiring all air crew arriving at the city's airport from Wednesday to provide throat saliva samples at a government facility nearby.