The number of daily new coronavirus cases in South Korea stayed under 300 for the third consecutive day Tuesday, but health authorities remain vigilant over a rise in patients in critical condition and cases with unknown transmission routes.

The country reported 235 new COVID-19 cases, including 222 local infections, raising the total caseload to 20,182, according to the Korea Centers for Disease Control and Prevention (KCDC).

The total caseload surpassed the 20,000 mark for the first time since the country reported its first case on Jan. 20.

Tuesday's daily tally marks a slight drop from 248 cases identified the previous day. Still, it marks the 20th consecutive day of triple-digit jumps since Aug. 14.

The country's daily tally of COVID-19 cases went down for the fifth straight day after it reached a near six-month high of 441 cases Thursday. South Korea reported 371 cases Friday, 323 cases Saturday and 229 cases Sunday.

Health authorities said strengthened social distancing, adopted over the weekend, has shown a slight positive impact in decelerating the virus spread, but the country is expected to witness an increase in both deaths and new daily COVID-19 patients in critical condition.

The KCDC said the number of COVID-19 patients in critical condition came to 104, up 25 from a day earlier. The number is also more than an 11 times increase from two weeks earlier.

Of the total, 65 of them, or 62.5 percent, have underlying illnesses, and only one of them was without any previous record of diseases, the KCDC said, adding that the study is ongoing on 34 others.

"It is worrisome that more than 30 percent of the confirmed COVID-19 patients over the past two weeks are those aged more than 60," Vice Health Minister Kim Ganglip said in a briefing. "The risk of dying due to the COVID-19 virus is highest among older people and those with underlying diseases."

Health authorities said the number of new COIVD-19 patients in critical condition has spiked as most of those who tested positive recently were 60 years old or above, an age group that is more likely to show critical health complications caused by the deadly virus.

The country's virus fatality rate currently stands at 1.61 percent, while the rate came to to 20.48 percent for those in their 80s, 6.49 percent for those in their 70s and 1.39 percent for those in their 60s, the KCDC said.

Meanwhile, the fatality rate of COVID-19 patients suffering from existing diseases, such as high blood pressure and diabetes, came to a whopping 97.2 percent, the KCDC said.

Amid growing calls for measures to prevent a possible shortage of hospital beds for COVID-19 patients in critical condition, health authorities said they have secured more such rooms in consultation with major general hospitals.

The authorities expect a maximum of 130 COVID-19 patients with severe symptoms that require treatment facilities such as oxygen treatment to occur daily by Thursday.

Of a total of 43 beds for COVID-19 patients in critical condition across the country, only nine in the wider Seoul area are currently open for admission.

Of the 238 locally transmitted cases, 175 were identified in the capital area, home to half of the country's 51 million population. Seoul added 93 more cases, while the surrounding Gyeonggi Province and west port city of Incheon reported 60 and 22 cases, respectively.

Other major municipalities reported additional infections, with the southwestern city of Gwangju adding four cases and the central city of Daejeon adding eight cases.

A total of 1,083 cases have been traced to the Sarang Jeil Church in northern Seoul -- a hotbed of the recent spike in new infections -- up 27 from a day earlier. The church-linked cases also led to infections in at least 26 locations, with 170 infected people.

A total of 419 patients have been reported from the Aug. 15 demonstration in central Seoul, up 20 from a day earlier, with cases identified not only in the greater Seoul area but in different provinces and municipalities across the country.

A church in Yeongdeungpo Ward, western Seoul, has so far reported 34 cases, up five from a day earlier, the KCDC said.

South Korea began to impose strengthened antivirus curbs in the greater Seoul area Sunday to stop the nationwide spread of COVID-19. More than 70 percent of virus cases in the country have come from the nation's capital area in recent weeks.

Under enhanced guidelines, restaurants and bakeries in the greater Seoul area can operate until 9 p.m., and only takeaway and delivery will be permitted from 9 p.m. to 5 a.m.

For franchise coffee chains, only takeout or delivery will be permitted regardless of operating hours.

Indoor sports facilities, such as fitness centers and billiard halls, are also advised to suspend their operations, while toughened virus prevention measures are also enforced at cram schools and elderly care centers.

Also health authorities are particularly concerned over a rising number of untraceable cases. Of the cases confirmed between Aug. 18 and Monday, a record 22.7 percent of them had unclear transmission routes, according to the KCDC.

The KCDC said a total of 155 COVID-19 patients in critical condition in 36 hospitals have been administered with remdesivir, an experimental drug conventionally used for Ebola.

The medication developed by US pharmaceutical giant Gilead Sciences Inc. started to be supplied to treat COVID-19 patients here earlier last month.

Health authorities also said they have begun using remdesivir for all aged patients who are hospitalized starting from Monday after a brief shortage due to supply issues late last month.

The number of newly identified imported cases stood at 13, with four of them detected at quarantine checkpoints at airports and harbors. The country's total number of imported cases is now at 2,836.

The total number of people released from quarantine after making full recoveries stood at 15,198, up 225 from the previous day. (Yonhap)