South Korea's health authorities warned on Monday that the country's daily virus cases may top 900 next week as a string of cluster infections from private gatherings and infection-prone facilities continued amid a surge in untraceable infection cases. They will streamline test procedures for quick results to rein in fast spread of the new coronavirus.

The country added 615 more COVID-19 cases, including 580 local infections, raising the total caseload to 38,161, according to the Korea Disease Control and Prevention Agency (KDCA).

Monday's tally marks the second consecutive day that the daily caseload topped 600. Four additional coronavirus fatalities were reported, bringing the total to 549.

The sharp uptick in daily new virus cases forced health authorities to raise the level of the country's social distancing measures by one notch to 2.5, the second highest under the five-tier system, in the greater Seoul area Tuesday for next three weeks.

The third-highest level of 2 will be applied for the other areas.

"The current situation is the biggest crisis in the country's virus fight, and the current outbreaks are not confined to specific areas," Na Seong-woong, a senior health official, said during a briefing. "Should the current pace continue, we may report daily new cases of over 900 next week after seeing new virus cases ranging from 550 to 750 this week."

Health authorities said they will adopt quick and accurate epidemiologic investigation by increasing the number of agents and introduce a saliva test.

It will also ease the criteria to release patients from quarantine by reducing the period of isolation to 10 days from 14 days, in order to address a deepening bed shortage for critically ill virus patients.

What is worrisome is that the proportion of virus cases without clear transmission routes stood at 17.8 percent for the past two weeks, sharply up from 15.8 percent a day earlier.

"Unless we curb the spread of the virus in the greater Seoul area under Level 2.5, we will see an explosive spread of virus infections and the country's medical system will falter, which could cause the social distancing level to be raised to Level 3 in all areas," Health Minister Park Neunghoo said at a meeting of the Central Disaster and Safety Countermeasure Headquarters.

The country's social distancing level was raised to Level 2 in the greater Seoul area about two weeks ago, which includes the suspension of entertainment facilities, such as nightclubs.

Starting Dec. 1 for one week, the authorities implemented additional restrictions on saunas, aerobic centers and similar facilities where COVID-19 could easily be spread.

The toughened social distancing steps, however, failed to rein in the accelerating spread of the new virus in the greater Seoul area.

Under the Level 2.5, gatherings with 50 or more people are prohibited, while door-to-door sales businesses, karaoke rooms, indoor fitness facilities and indoor concert venues that offer standing shows will be forced to close, in addition to nightclubs and bars.

Restaurants cannot receive customers after 9 p.m. but can offer takeout and delivery. Cafes are only allowed to serve takeout at all hours.

Movie theaters, internet cafes, private academies, study halls, amusement parks, beauty salons, barber shops, large grocery stores and department stores cannot operate past 9 p.m.

The nighttime curfew for those facilities has already been in place in Seoul since Saturday, as the city government sought to preemptively curb the soaring infections in the capital area. The city's public transportation service was also reduced by 30 percent.

Sports events are allowed without spectators while religious services are only available online or via broadcasts. In-person religious activities, if needed, are permitted with 20 or less participants.

By region, 231 confirmed cases were reported in Seoul and 154 from the surrounding Gyeonggi Province. Incheon, west of Seoul, added 37 more cases. The greater Seoul area is home to about half of the country's 51.6 million population.

The number of imported cases came to 35, up from 32 the previous day. They include 12 from the United States and nine from Europe.

The number of COVID-19 patients with serious symptoms across the country reached 126, up from 125 on Sunday.

The total number of people released from quarantine after making full recoveries stood at 29,301, up 173 from Sunday. (Yonhap)