SEOUL — South Korea reported 142 more coronavirus cases on Saturday, the sharpest spike in infections yet, with many new cases involving patients being treated in hospital for mental health issues.

The national toll of 346 is now the second-highest outside of China, with the jump in cases at the hospital in the southern city of Cheongdo following a similar spike among members of a religious sect in the nearby city of Daegu.

Among the new cases, 92 were "related" to patients or staff at Cheongdo Daenam Hospital, the Korea Centers for Disease Control and Prevention (KCDC) said.

"Most of the hospital's patients who have been diagnosed are those who had been staying as inpatients for mental illnesses," Seoul's vice health minister Kim Gang-lip told reporters.

Some cases show "no confirmed epidemiological connections", meaning they are not sure where or how they contracted the virus, he added.

Authorities reported another death on Saturday, taking the toll to two. Both victims had been inpatients at the hospital.

Almost 170 members of the Shincheonji Church of Jesus have now been infected, starting with a 61-year-old woman who attended at least four services at the church's Daegu branch before being diagnosed.

"Those who are related to Shincheonji's Daegu branch account for 48 percent of all confirmed cases," KCDC director Jung Eun-kyeong told reporters.

KCDC said some 9,300 Shincheonji members in Daegu have either been quarantined at facilities or have been asked to stay at home. Among them, 1,261 said they had symptoms, health officials added.

The mayor of Daegu — South Korea's fourth-biggest city, with a population of over 2.5 million — has advised locals to stay indoors, while access to a major US military base in the area has been restricted.

One of the Shincheonji members in Daegu visited China — where the deadly virus was first detected — in January, while some three others are believed to have traveled to other countries, KCDC director Jung said.

Cheongdo, some 27 km south of Daegu, is the birthplace of Shincheonji's founder Lee Man-hee.

County officials said on Friday that a three-day funeral was held for one of the church members three weeks ago at a hall owned by the Cheongdo hospital.

Shincheonji is often accused of being a cult and claims its founder Lee has donned the mantle of Jesus Christ and will take 144,000 people with him to heaven on the day of judgement.

But with more church members than available places in heaven, they are said to have to compete for slots and pursue converts persistently and secretively.

President Moon Jae-in on Friday called for a "thorough investigation" of everyone who attended the funeral and Shincheonji services.

The central government on Friday had declared Daegu and Cheongdo "special management zones", with Prime Minister Chung Sye-kyun saying the region would be supported with medical personnel, beds and equipment.

Authorities in Seoul banned public rallies at three main locations on health and safety grounds.

The US army garrison in Daegu — where around 10,000 soldiers, civilians and family members live or work — has restricted access and instructed any American troops who recently attended Shincheonji services to self-quarantine.

Shincheonji offered an apology, suspending its worship services and gatherings nationwide.

"We are deeply sorry that because of one of our members, who thought of her condition as a cold because she had not traveled abroad, led to many in our church being infected and thereby caused concern to the local community," it said in a statement.

But its leader Lee told his followers the outbreak had been "caused by the Devil" and compared it to the biblical testing of Job, Yonhap news agency reported. — aFP