JERUSALEM — Concerns of a widening threat from coronavirus are growing as millions of Israelis are preparing to gather at polling places for national elections next week, after reports that a group of South Koreans who had visited some of the country's most popular religious and tourist spots tested positive for the infection.

Dozens of students who might have been in proximity to the South Korean tourists were directed to stay in home-based quarantine for two weeks, as were hotel housekeepers and employees of Masada, Tel Beer Sheva and other national parks. Israeli officials, who had expressed cautious optimism that Israel could avoid significant risk from the global epidemic, immediately increased restrictions on those entering the country.

Non-Israeli travelers from South Korea and Japan have been barred from entering, according to local media reports, and Israelis arriving from any of several Asian countries face two weeks of mandatory quarantine. Officials added South Korea and Japan to the list, which had included China, Hong Kong, Thailand, Singapore and Macao.

Authorities scrambled to address the sudden increase in risk. A Health Ministry official released the itinerary of the South Korean group at a hastily called news conference Saturday night and beseeched anyone who might have been within six feet of the group for at least 15 minutes to isolate themselves for two weeks. As many as 200 people reportedly entered quarantine based on that criteria.

Others who might have overlapped with the group from a greater distance were advised to monitor themselves for fever or other symptoms of covid-19 infection.

“We have an opportunity here to stay on top of the virus,” said Moshe Bar Siman Tov, the ministry’s deputy director, according to the Jerusalem Post. “The potential that someone caught the virus from the tourists is high; whoever doesn’t enter quarantine is endangering the public.”

The group of 77 South Koreans was reportedly on a nine-day pilgrimage of Christian sites in Israel and the West Bank, including more than a dozen churches in Jerusalem’s Old City, Bethlehem and Hebron. It was only after the group flew home in mid-February that nine tested positive for the virus. The South Korean government alerted Israel.

The move to bar Korean travelers sparked complaints from Seoul, where officials reportedly summoned the Israeli chief of mission to explain after some 200 South Korean nationals were turned away at Ben Gurion Airport. Cases of coronavirus infection have surged in South Korea in recent days. Most of the infections centered on a religious community in the southern city of Daegu.

News of the South Korean travelers’ visits to crowded sites in Israel came as the country reported its first confirmed case of coronavirus infection. One of nine Israeli passengers who was flown home from a cruise ship stranded in Japan tested positive for the virus Friday.

Fear of an outbreak here is growing as the country prepares for its third national election in less than a year, raising concerns that voters already exhausted from the country’s prolonged political stalemate will be scared away from crowded polling places. Prime Minister Benjamin Netanyahu’s Likud party and Benny Gantz’s Blue and White coalition fought to inconclusive results in April and September, with neither leader able to form a government.

Orly Ades, head of Israel’s Central Elections Committee, told Army Radio on Sunday that 20 polling stations will be readied for voters in isolation due to possible exposure to the virus.

Public Security Minister Gilad Erdan said police were preparing for the possibility of disruptions to voting caused by fear of the virus, including the spread of rumors or deliberately false information, according to reports. He said officers would enforce the Health Ministry’s quarantine orders if those implicated refused to comply.