South Korea's daily new virus cases stayed in the 700s for the third day in a row Monday, as health authorities warned against the spread of the more contagious delta coronavirus variant.

The country reported 711 more COVID-19 cases, including 644 local infections, raising the total caseload to 160,795, the Korea Disease Control and Prevention Agency (KDCA) said.

The latest figure is down from 826 on Friday, 794 on Saturday and 743 on Sunday, and a nearly six-month high due to the sharp spike in new cases in the Seoul metropolitan area.

The country added two more COVID-19 deaths, raising the death toll to 2,028.

New cases spiked to close to levels unseen since January, when the nation was gripped by the third wave of the pandemic, with many cases from schools, private institutions, restaurants, indoor gyms and entertainment venues.

New cases in the greater Seoul area, home to half of the nation's 51 million population, have accounted for over 80 percent of the total over the past 10 weeks, and nearly half of them were in their 20s and 30s, the KDCA said.

Sohn Young-rae, a senior health ministry official, told TBS radio that the spread of the delta variant, which was first identified in India, is "rapidly increasing" in South Korea.

Currently, the delta variant accounts for about 7 percent of new COVID-19 infections, compared with less than 1 percent two months ago, Sohn said.

The nation's daily average of local COVID-19 infections stood at 655 people over the past week, up 33.2 percent from a week earlier, the KDCA said.

About 80 percent of new infections came from Seoul and its neighboring areas, with people in their 20s and 30s, most of whom are not eligible for vaccinations, fueling new cases, it said.

South Korea had planned to allow vaccinated people to take off their masks outdoors, but the plan was scrapped as new infections jumped in the greater Seoul area.

The KDCA said it eased some guidelines for fully vaccinated people Monday. For fully vaccinated people, they will be required to get a COVID-19 test if they come into contact with an infected person. Previously, they were required to get three rounds of COVID-19 tests.

A total of 15.35 million people, or 29.9 percent of the country's population, have received their first shots of COVID-19 vaccines. The KDCA said 5.32 million people have been fully vaccinated, taking up 10.4 percent of the population.

The country currently administers two-dose vaccines from AstraZeneca, Pfizer and Moderna, as well as Janssen's single-shot vaccine.

Of the newly confirmed domestic cases, 301 were from Seoul, 210 from the surrounding Gyeonggi Province and 16 from the western port city of Incheon.

There were 67 additional imported cases, with 60 of them from Asian nations, excluding China.

The total number of people released from quarantine after making full recoveries was 150,044, up 430 from a day earlier. (Yonhap)