SEOUL, Dec 16 (Reuters) - South Korea said on Thursday it will reinstate stricter social distancing rules a month-and-a-half after easing them under a "living with COVID-19" policy, as the number of new infections and serious cases spirals. Curbs will return from Saturday to Jan. 2, limiting gatherings to no more than four people - as long as they are fully vaccinated - and forcing restaurants, cafes and bars to close by 9 p.m. and movie theatres and internet cafes by 10 p.m., officials said. Unvaccinated people can only dine out alone, or use takeout or delivery services. The measures come as South Korea"s daily coronavirus tallies and the number of serious cases continue to make new records amid a persistent spike in breakthrough infections, adding to strains on the country"s medical system. "We"re making all-out efforts to overcome the pressing crisis by expanding our medical capacity and vaccination campaign, but we need time," Prime Minister Kim Boo-kyum told an intra-agency meeting. "We can go beyond this crisis only by beating down the current spread as soon as possible through strong social distancing." The Korea Disease Control and Prevention Agency (KDCA) reported 7,622 cases for Wednesday, a day after posting a new record daily count of 7,850. The number of serious cases hit another fresh high at 989, with some 87% of intensive care unit beds taken up in the Seoul metropolitan area and about 81% in use nationwide. More than 92% of South Korean adults are fully vaccinated, but the number of new cases has surged nearly five-fold since the rules were eased last month, while the number of serious cases has tripled. Currently, businesses have no limits on operating hours, and private gatherings are confined to six people in the greater Seoul area and eight in other regions, regardless of vaccination status. If people dine out, all but one must be fully vaccinated. Daily numbers of cases shot past 7,000 for the first time last week, just days after surpassing the 5,000 mark. KDCA director Jeong Eun-kyeong said the daily tally could top 10,000 this month if the upturn is not blunted. Total infections rose to 544,117, including 148 cases of the potentially more transmissible Omicron variant, with 4,518 deaths, the KDCA said.