SEOUL, July 14 (Reuters) - South Korea on Wednesday (Jul 14) tightened social distancing curbs across most of the country to try to combat its worst-ever outbreak of coronavirus after new COVID-19 cases on Tuesday soared past previous daily peaks to 1,615.

Amid growing concerns over the more contagious Delta variant and a stagnating vaccine rollout, the latest daily tally easily surpassed the previous record - last Friday's 1,378. Cluster infections have spread rapidly around the capital Seoul and neighbouring areas fuelled 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 per cent of all new cases reported from Jul 4 to 10, and nearly 70 per cent of more transmissible strains, the KDCA said.

The outbreak has so far brought fewer deaths and serious patients 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 per cent of the 52 million population having received at least one dose of vaccine, whereas comparable numbers exceed 60 per cent in many other advanced nations including Britain and Singapore.