South Korea's new Covid-19 cases stayed above 7,000 for the fourth consecutive day on Saturday and critical cases surged to a record high as the government reimposed restrictions to contain the fast spread of the virus.

The country added 7,314 more Covid-19 cases, including 7,284 local infections, bringing the cumulative total to 558,864, the Korea Disease Control and Prevention Agency (KDCA) said.

Saturday's tally is slightly down from the previous day's 7,434 and the record high of 7,850 reported on Wednesday, reports Yonhap News Agency.

The number of critically ill patients hit an all-time high of 1,016, surpassing the grim milestone of 1,000 for the first time.

The previous daily high was 989 on Thursday.

Deaths from the virus rose by 53, bringing the total to 4,644. The fatality rate stood at 0.83 per cent.

The country reported 15 more cases of the omicron variant, putting the total at 166.

The government reimposed a set of revised virus restrictions across the country Saturday, which will remain in effect until Jan. 2 to stem the spread of the virus.

It marks a reversal of the government's "living with Covid-19" scheme that began last month with an aim to regain normalcy by relaxing virus restrictions in phased steps.

Under the updated measures, the maximum size of private gatherings is limited to four people nationwide, from the current limit of six in the capital area and eight elsewhere.

And a 9 p.m. or 10 p.m. curfew is applied to businesses, depending on their type of service.

Only fully vaccinated people are allowed to use restaurants and cafes with other people, while those who have not been vaccinated can only use the facilities alone or request takeout or delivery.

Schools in the greater Seoul area will resume remote learning and run at about two-thirds or 75 percent capacity beginning on Monday, except for first and second grades in elementary school.

The extent to which masks can be worn and whether there is eating inside determine the degree of restriction. Up to 300 people can gather for outdoor sports events and other festivals approved by government agencies.

Of the locally transmitted cases, Seoul reported 2,794 infections and Gyeonggi Province that surrounds the capital logged 2,041 cases Saturday.

The KDCA said 30 cases came from overseas, raising the caseload to 16,266.