SEOUL: South Korea raised its coronavirus alert to the second-highest level in Seoul and surrounding areas Sunday as authorities struggle to contain a fresh outbreak.

The country largely brought the virus under control with a "trace, test and treat" approach, but in recent weeks new infections have jumped from around 100 a day to more than 500.

South Korea confirmed 631 new cases on Sunday -- the highest in nine months -- with the majority in the greater Seoul region, according to the Korea Disease Control and Prevention Agency.

By global standards the figure remains low, but the rise has alarmed authorities, who have tightened social distancing measures.

"We are facing the biggest crisis in our fight against Covid-19," Prime Minister Chung Sye-kyun said Sunday.

All gatherings of more than 50 people will be banned and professional sports will be held behind closed doors with no spectators.

Cafes will continue to serve only takeaways, while restaurants must close by 9 pm, with only deliveries permitted afterwards.

The tightened measures will be in place until the end of the year, Chung said.

Sunday's figures take the total number of cases in the country to more than 37,000.

South Korea endured one of the worst early Covid-19 outbreaks outside mainland China, but never imposed the kind of lockdowns ordered in much of Europe and other parts of the world.

The country has previously been held up as a model of how to combat the virus, and the public has largely followed social distancing and other rules, such as wearing face masks.