Seoul this month switched to a 'living with COVID-19' plan aimed at lifting rigid distancing rules and ultimately reopening after reaching vaccination goals last month.

Looking at the metropolitan Seoul area alone, the situation is critical enough to impose an emergency plan at any time, Prime Minister Kim Boo-kyum told a coronavirus response meeting.

The Korea Disease Control and Prevention Agency said the emergency plan may be imposed if and when the nationwide use of ICU beds surpasses 75 per cent.

Risk assessments reviewing medical response shortfalls, surges in the number of elderly patients and the uptake in booster shots may also come into play.

Hospitals were treating 586 severe COVID-19 patients as of midnight on Tuesday, rapidly filling up limited hospital beds for serious and critical cases.

More than 85 per cent of them were aged 60 or above, KDCA data showed.

At least 69 per cent of ICU beds were filled nationwide, and 83 per cent in capital Seoul and neighbouring areas, as the health authorities have been rushing to secure more beds.

Despite the increase in hospitalisation rate, the country's mortality rate remains relatively low at 0.79 per cent.

South Korea was one of the first countries to record COVID-19 cases after the virus emerged in China in late 2019. It has since had 425,065 infections, with 3363 deaths.

The country has fully vaccinated 79.1 per cent of its 52 million people.

Australian Associated Press