South Korea announced its highest number of new coronavirus cases for more than a month Monday, driven by an infection cluster in a Seoul nightlife district just as the country loosens restrictions.

The nation has been held up as a global model in how to curb the virus, but over the weekend its capital -- as well as neighbouring Gyeonggi province and the nearby city of Incheon -- ordered the closure of all clubs and bars after a burst of new cases sparked fears of a second wave.

The news comes as parts of Europe begin a cautious re-opening, with health experts warning that moving too quickly will result in a surge in infection numbers. The country reported 35 new cases Monday, taking its total to 10,909, according to the Korea Centers for Disease Control and Prevention -- after recording only single-digit increases for eight of the preceding 12 days, many of them overseas arrivals.

As of Monday morning, a total of 85 cases so far have been linked to a 29-year-old man who tested positive after spending time at five clubs and bars in the Itaewon area in early May, Seoul Mayor Park Won-soon tweeted.

City authorities are urging everyone who visited the district over a two-week period to get tested, he told a radio station.

But health officials are struggling to trace "thousands of people" who went to clubs and bars in Itaewon, said Prime Minister Prime Minister Chung Sye-kyun.

"The majority of the visitors are not reachable," Chung said, urging all of them to get tested. "If you hesitate a single day, our daily clock may stop for a month. Please contact the nearest clinic or health centre right now."

The spike in new infections came as everyday life in South Korea returns to normal, with the government relaxing social distancing rules last Wednesday. The country endured one of the worst early outbreaks of the disease outside mainland China, and while it never imposed a compulsory lockdown, strict social distancing had been widely observed since March.

But it appeared to have brought its outbreak under control thanks to an extensive "trace, test and treat" programme that has drawn widespread praise. Facilities such as museums and churches have reopened and some professional sports -- including baseball and soccer -- have started new seasons, while schools are set to re-open starting this week.