The number of coronavirus cases in South Korea increased to 2,022 on Friday, with a total of 13 fatalities as the nation aggressively counters the fast-spreading virus with massive testing, particularly for 210,000 followers of a religious sect at the centre of the epidemic.

The 256 new cases brought the nation's total infections to 2,022, the Yonhap News Agency quoted the Korea Centers for Disease Control and Prevention (KCDC) as saying.

Only two days ago, the number of infections exceeded 1,000.

More than half of newly confirmed cases were linked to a branch of the Shincheonji Church of Jesus in the southeastern city of Daegu, 300 km southeast of Seoul.

Of the 256 new cases, 182 are in Daegu, and 49 are in the neighbouring North Gyeongsang Province.

Since raising the virus alert level to "red", the highest level, on Sunday, health authorities have focused on halting the spread of the virus in Daegu, the epicentre of the virus outbreak in South Korea, and North Gyeongsang.

Experts said the number of confirmed cases is expected to jump in the coming days as health authorities have begun testing more than 210,000 members of the Shincheonji Church of Jesus.

The government also ordered another 1,638 Shincheonji followers to self-isolate as they have shown symptoms, Yonhap News Agency said in its report.

Since the first coronavirus case -- a Chinese woman from Wuhan, the epicentre of the outbreak -- on January 20, the pace of infections had not been alarming until February 18, when a 61-year-old woman who is tied to the Daegu religious sect tested positive for the virus.

Since then, the nation has seen an explosion in infections as it accelerated virus tests on potential cases.