SEOUL –

South Korea tightened social-distancing measures across most of the country on Wednesday to try to combat its worst-ever outbreak of COVID-19, after new cases soared past previous daily peaks Tuesday to 1,615.

Amid growing concerns over the more contagious delta variant and a stagnating vaccine rollout, the latest daily tally easily surpassed last Friday's previous record of 1,378. Cluster infections have spread rapidly around the capital, Seoul, and neighboring areas fueled by the delta variant, the Korea Disease Control and Prevention Agency (KDCA) said.

Prime Minister Kim Boo-kyum said from Thursday the government would tighten distancing rules across most of the country, with the exception of some southern regions, to Level 2 on the country's four-level scale. Under level 2, gatherings of more than eight people are banned, and restaurants and bars must close by midnight.

That's still two levels below the toughest curbs available to the government. Those restrictions — Level 4, including a ban on gatherings of more than two people after 6 p.m — were imposed from Monday in the greater Seoul area.

The ongoing surge in new cases was partly fanned by the rise of the delta variant, which accounted for 30.7% of all new cases reported from July 4-10, and nearly 70% of more transmissible strains, the KDCA said.

The outbreak has so far brought fewer deaths and patients in a serious condition than earlier ones, with many older and more vulnerable South Koreans now vaccinated against the virus. The country's total infections in the pandemic rose to 171,911, with 2,048 deaths, KDCA data showed.

But the inoculation drive has slowed in recent weeks, with just 30.6% of the 52 million population having received at least one dose of vaccine, whereas comparable numbers exceed 60% in many other advanced nations including the U.K. and Singapore.