Hong Kong medical experts urged the government to immediately tighten social distancing measures and launch large-scale virus testing in the community to trace undiscovered COVID-19 cases, as the city on Monday recorded 73 new infections, the highest daily count over the past three months.

As of Monday, the city's total tally stood at 5,701, with 108 related deaths. Separately, more than 70 people have tested positive preliminarily for COVID-19, according to health authorities.

The resurging pandemic is mainly linked to 21 dance clubs scattered across Hong Kong. According to the Centre for Health Protection of the Department of Health, so far 132 confirmed patients, including 50 of them confirmed on Monday, were linked to the dancing cluster, the largest cluster since the pandemic struck in January.

Facing the spike in new cases, the government issued a mandatory testing notice for the first time, requiring anyone who had visited any of the 21 dancing venues between Nov 1 and 21 to undergo a virus test before Nov 24.

Anyone who fails to comply with the mandatory testing notice will face a fixed HK$2,000 ($258) penalty. Violators will be given a testing order and those who fail to comply will be liable to a HK$25,000 fine and imprisonment for six months.

Doctor Leung Chi-chiu, chairman of the advisory committee on communicable diseases of the Hong Kong Medical Association, on Monday said that the administration must take immediate action to tighten the city's social distancing rules and minimize local transmissions. Leung proposed to suspend on-campus classes, resume practices of working from home, and close entertainment venues and sports facilities, measures seen as effective ways to contain the virus at the height of the city's last wave of the pandemic in July.

The government will also need to introduce mass virus screening to identify patients infected with COVID-19 as early as possible, and trace local transmission routes and sources, Leung told China Daily.

"Only in this two-pronged approach can the city effectively contain the fourth wave of the outbreak," he said.

Leung said that with the volatile pandemic situation, the government has to "learn a lesson" from the new wave. The authorities should thoroughly review its coronavirus prevention and control measures, especially those for people who arrive in the city from outside Hong Kong as well as quarantine-exempted groups, to plug loopholes, he said.

Leung also urged the government to closely cooperate with some high-risk industries, providing industry practitioners with working guidelines, setting up a mechanism to report patients with respiratory symptoms in a timely manner and providing regular mandatory virus testing for high-risk groups.

In an interview with Radio Television Hong Kong, Benjamin Cowling, head of the division of epidemiology and biostatistics at the University of Hong Kong's School of Public Health, reckoned that the government should close bars, karaoke venues, gyms and other indoor leisure facilities.

Employers should consider work-at-home policies and the government needs to consider tighter restrictions in restaurants, he said.

On the same day, the city welcomed its first batch of returnees from Guangdong province and Macao under a quarantine-free program that began on Monday.

Those eligible should apply for an exemption and choose returning dates via an online booking system. Returnees must show negative COVID-19 test results granted 24 hours before traveling when they enter the city.

According to the government, as of last Friday, more than 11,470 people had applied for the program between Nov 23 and 29. Around 2,140 residents returned to Hong Kong under the program on Monday.

Due to the surge of new coronavirus infections in Hong Kong, the city and Singapore postponed the world's first quarantine-free travel bubble for two weeks. Given the postponement, the inaugural flights between the two places, originally scheduled to depart on Nov 22, were delayed. The details of the formal reintroduction of the plan will be announced early next month.