HONG KONG, Nov. 21 (Xinhua) -- Hong Kong on Saturday reported the highest number of daily new cases of COVID-19 in about three months, with the authorities toughening up measures to fend off a new wave of the coronavirus outbreak.

The Center for Health Protection (CHP) said there were seven new imported cases and 36 local infections detected on Saturday, including 13 with unknown origins.

Meanwhile, over 60 people tested positive for COVID-19 primarily.

Head of the CHP's Communicable Disease Branch Chuang Shuk-kwan said the new cases have been rising rapidly in recent days, and warned of a fourth wave of the epidemic outbreak.

In the face of the resurgence of COVID-19 cases, the government of the Hong Kong Special Administrative Region (HKSAR) has tightened social distancing measures including banning live performance in bars and nightclubs and suspending in-person learning for grade 1-3 primary school students.

To reduce imported cases, the government also raised the threshold for the crew members of flights to obtain exemption of quarantine. Among the new requirements starting Sunday is that they must have a negative testing result within 48 hours and take another test after arriving in Hong Kong.

Data showed crew members of flights accounted for about 93 percent of all the visitors exempted from quarantine in Hong Kong every day.

The exemption policy for other visitors including sailors of cargo ships was also tightened.

HKSAR Chief Executive Carrie Lam has said in a social media post that the situation was "fairly severe" and pledged more testings to cut transmission chains.

Due to the worsening epidemic, the bilateral Air Travel Bubble between Hong Kong and Singapore due to start on Sunday will be postponed for two weeks and the launch time will be subject to the situation of the epidemic.