SEOUL (NYTIMES) - The Prime Minister of South Korea said on Sunday (Sept 26) that the nation would soon start administering Covid-19 booster shots to medical workers and people in their 60s and older, as the country battled a new wave of infections after a national holiday.

South Korea has seen a spike in infections in recent days as millions of people returned home after Chuseok, a three-day holiday celebrating the autumn harvest.

On Sunday, Prime Minister Kim Boo-kyum said the vaccination campaign would speed up.

More than 85 per cent of new cases in the past couple of weeks were people who had not been fully vaccinated, he said. Details of the new plan will be announced on Monday.

"We feel the sharp repercussions from the mass migration during the Chuseok holiday," Mr Kim said. "We had anticipated this to a degree, but we face a serious situation, given the scale and speed of the increase in new cases."

South Korea warned earlier this month that its surge in cases tied to the Delta variant jeopardised plans to return to a more normal way of life in November.

The nation has already started relaxing some restrictions, including allowing restaurants and bars to stay open until 10pm, as vaccinations have picked up.

But more than 18 months into the pandemic, there is growing fatigue, and the government is unsure how strictly South Koreans are following the measures.

South Korea will also start to administer shots to teenagers and pregnant women, Mr Kim said. Currently, anyone 18 or older is eligible to be vaccinated.

Starting next month, the interval between the first and second shots will also be shortened, he said.

So far, about 45 per cent of the total population is fully vaccinated, and about 74 per cent is partially inoculated, according to the government's latest data.

South Korea reported a record 3,273 new cases on Saturday, after hovering near 2,000 cases before the holiday.