South Korea's new coronavirus cases fell below 4,000 on Thursday, a day after hitting an all time-high of 4,115. But critical cases and deaths climbed to fresh highs, fueling worries about the virus spread ahead of another pandemic winter.

The country reported 3,938 new COVID-19 cases, including 3,917 local infections, raising the total caseload to 429,002, according to the Korea Disease Control and Prevention Agency (KDCA).

Critically ill patients hit an all-time high of 612, up 26 from the previous record set a day earlier. The same figure averaged 498 for the seven days ending Sunday.

The country added 39 more deaths from COVID-19, the highest number since the start of the fourth wave of the pandemic in July, bringing the death toll to 3,401, with the fatality rate standing at 0.79 percent.

Daily infections soared as the government began easing virus restrictions on Nov. 1 for a gradual return to pre-pandemic life under the three-phase "living with COVID-19" scheme.

South Korea planned to move to the second stage in mid-December, but health authorities have warned the country may not be able to do so if the current trend continues.

The government is struggling to secure enough hospital beds, especially in the greater Seoul area, as infections remain high and the number of critically ill patients is on the rise.

Health authorities said Wednesday that the rate of COVID-19 patients who deteriorate to serious conditions rose to 2.05 percent in October, up from 1.53 percent in September. The rate for November is predicted to pass 2.36 percent.

"It is moving beyond our prediction range," Son Young-rae, a senior health official, said during a briefing, adding the government had expected to see such rates only when the daily infections surpassed 5,000.

The KDCA said 79.3 percent of the country's 52 million population are fully inoculated and 82.5 percent have received their first shots. (Yonhap)