South Korea's daily new coronavirus cases stayed around 700 on Thursday, as sporadic infections across the country complicate antivirus efforts, prompting authorities to mull tougher virus curbs to contain the pandemic.

The country reported 698 more COVID-19 cases, including 670 local infections, raising the total caseload to 112,117, the Korea Disease Control and Prevention Agency (KDCA) said.

Thursday's daily caseload was down from 731 the previous day, which marked the highest since Jan. 7.

The country added six more deaths, raising the total to 1,788.

Health authorities have expressed concerns over a fourth wave of the pandemic in spring as people let their guard down and increase activities, warning of tougher rules on multiuse facilities and business operations if the current trend continues.

The number of locally transmitted cases surpassed 600 over the past week for the first time in three months, and the proportion of untraceable virus cases stood at 28.2 percent during the period, the KDCA said.

Last week, the country decided to maintain the current level of social distancing rules through May 2 to contain the virus, while banning operations of entertainment establishments in the greater Seoul area and the southeastern port city of Busan.

The greater Seoul area, home to half of the nation's 52 million population, is under the Level 2 distancing scheme, the third highest in the five-phase system. The rest of the country is under Level 1.5, except for some municipalities that have adopted Level 2 measures.

Restaurants in the capital area are allowed to have dine-in customers until 10 p.m. under the current guidelines, but officials said they could shorten their business hours if daily cases rise further.

The KDCA said 104 new vaccination centers opened Thursday, which would scale up the daily vaccinations from the current 30,000 to over 70,000.

To detect patients at an early stage, health officials said they will expand preemptive testing to detect patients and explore ways to effectively use self-testing kits to further step up the testing capacity.

Minister of the Interior and Safety Jeon Hae-cheol said the number of health regulation violations in multiuse facilities has been rising, saying authorities will step up monitoring on virus-prone facilities, including restaurants, cafes, saunas and child care centers.

Since the country started its vaccination program on Feb. 26, a total of 1,285,909 people, or 2.47 percent of total population, have been given COVID-19 vaccine shots, including 45,520 the previous day.

AstraZeneca's vaccine has been given to 951,712 people, while 334,197 received that of Pfizer.

The KDCA said 60,569 people have received two doses.

A total of 11,927 cases of side effects after vaccinations have been reported, up 128 from a day earlier, but 98.4 percent were mild symptoms, including muscle pain and fever.

Two more deaths after vaccinations were reported, raising the total to 51, according to the KDCA. Authorities, however, said most cases were not related to the vaccination.

South Korea plans to vaccinate 12 million people by the end of June to achieve herd immunity by November, but concerns are rising over delays in the inoculation drive after the US suspended use of the Johnson & Johnson vaccine over rare blood clots.

The country signed a contract with Johnson & Johnson for 6 million doses for its vaccine rollout, which was initially expected to be provided in the third quarter.

The health authority said it has not yet changed its procurement plan on the Johnson & Johnson vaccine, while closely monitoring its side effect and US reviews.

On Monday, health authorities resumed administering AstraZeneca vaccines to eligible recipients aged over 30, days after putting the program on hold amid growing concerns over its safety.

With only two types of vaccines currently available here, the health ministry earlier said it expects to secure Novavax vaccines as early as June, and 20 million doses will be ready by the third quarter. Novavax vaccines require two shots for immunization.

Of the newly confirmed locally transmitted cases, 216 came from Seoul, with Gyeonggi Province that surrounds the capital city accounting for 222.

Sporadic infections continued to pop up in various settings in the greater Seoul area, including sports facilities, churches, karaoke rooms, restaurants, workplaces and schools, complicating efforts to contain the virus.

The southeastern port city of Busan reported 54 new cases. A total of 435 patients have been traced to a bar in the country's second-largest city since the first confirmed case on March 24, up 17 from the previous day.

There were 28 additional imported cases, with 19 from Asian nations, excluding China, and four from Europe.

The number of seriously or critically ill COVID-19 patients was 99, one down from the previous day.

The total number of people released from quarantine after making full recoveries was 102,513, up 530 from a day earlier. (Yonhap)