The exact cause of death is being investigated, the Centers for Disease Control and Prevention said in a statement.

KCDC had initially announced 31 new cases of the virus on Thursday, but the additional cases take the overall number to 104.

Most of the new cases confirmed are in the city of Daegu where a person who was infected with the virus had attended church services and visited a hospital before testing positive.

Malls, restaurants and streets in Daegu, the country's fourth largest city with a population of 2.5 million, were largely empty in scenes that local social media users likened to a disaster movie.

"We are in an unprecedented crisis," Daegu Mayor Kwon Young-jin said at a briefing, as he warned of likely further cases.

He told residents to stay indoors as a surge in confirmed cases raised the prospect of wider transmission.

Kwon cautioned that at least 90 more of the around 1,000 other people who attended services at the Temple of the Tabernacle of the Testimony were also showing symptoms.

"We plan to test all believers of that church and have asked them to stay at home isolated from their families," Kwon said.

South Korea's vice health minister Kim Kang-lip said at a separate briefing in the administrative city of Sejong that the situation was "very grave."

The cases previously reported in South Korea had mostly involved people who had travelled individually to China or come in contact with somebody who had.

Daegu authorities ordered the shutdown of all kindergartens, while schools considered postponing the beginning of the spring semester scheduled for early March.

The Defence Ministry banned troops stationed in Daegu from leaving their barracks and receiving guests. The US military imposed similar restrictions on its army base in the city, which houses thousands of troops, family members and civilian employees.

Topics such as "Daegu lockdown" and "Daegu church" were among the top searches on major South Korean portal Naver as debate heated up online about whether the city should be sealed off from the rest of the country.

A KCDC official said the government was not yet considering that measure.

The church at the centre of the outbreak is a branch of the Shincheonji Church of Jesus, a religious movement founded in 1984 by South Korean Lee Man-hee who has about 500,000 followers.

Australian Associated Press