Churches were closed in South Korea on Sunday with many holding online services instead as authorities fought to rein in public gatherings, with 586 new coronavirus infections taking the tally to 3,736 cases.

That came a day after the biggest daily jump of 813 cases in South Korea's battle with the largest virus outbreak outside China, the Korea Centers for Disease Control and Prevention (KCDC) said. The death toll rose to 18.

In Seoul, the capital, about a dozen worshippers were turned away from the Yoido Full Gospel Church, which put a sermon for its 560,000 followers on YouTube, filmed with a small choir instead of all 200 members and 60-strong orchestra.

"I had heard there would be no service, but just came to check as I live nearby, but yes, it is so empty," said one of them, Song Young-koo, as he left South Korea's biggest church.

"It's a wise decision to do it online, since the virus would easily spread at mass gatherings and churches can be no exception."

Authorities have warned of a "critical moment" in the battle on the virus, urging people to refrain from attending religious services and political events and stay home this weekend.

For the first time in its 236-year history, South Korea's Catholic church decided to halt masses at more than 1,700 locations nationwide. Buddhist temples also called off events, while major Christian churches held online services.

Of the new cases, 333 were from the southeastern city of Daegu, the location of a church at the center of the outbreak, and 26 from the nearby province of North Gyeongsang, KCDC said.

The agency said some church members in January visited the central Chinese city of Wuhan, where the disease emerged late last year, adding that it was investigating to determine if the trip played a role in the outbreak.

"We're tracing back how many members had gone to China," its deputy director, Kwon Jun-wook, told a briefing.

"Our top priority is to find out how the coronavirus has been transmitted so widely among the Shincheonji followers," he added, in a reference to the church involved.

The numbers of cases was likely to continue growing in early March, he added, pledging greater efforts to rein in key infection sources.

At a news conference in Seoul a group of doctors and chiefs of public hospitals urged the government to combat a shortage of beds by assigning them to the critically ill, after two patients died in self-quarantine at home.

HELP FOR NORTH KOREA

President Moon Jae-in called for unity and vowed greater efforts, including an extra budget, to fight the outbreak, in a speech.

"The outbreak can threaten our lives temporarily, but it cannot break our unity and hope," he said.

Moon proposed joint efforts with North Korea to prevent an outbreak in the neighbor and improve healthcare.

North Korea has not confirmed cases, but has ordered a month in quarantine for those with symptoms, while state media said leader Kim Jong Un held a meeting on tougher measures.

The crisis spooked trade and financial markets, leading Samsung Electronics, Hyundai Motor and LG Display to temporarily shut down a plant each and prompting boy band BTS to cancel a world tour set for April.

More neighbors suspended flights and banned visitors from South Korea.

In a statement, the foreign ministry said Foreign Minister Kang Kyung-wha asked Washington to avoid "excessive action that could needlessly shrink exchanges between both countries," during a telephone call with U.S. Deputy Secretary of State Stephen Biegun on Sunday.

The request came after the United States advised Americans not to travel to hard-hit regions, such as Daegu.