SEOUL, South Korea -- Coronavirus cases more than doubled overnight in South Korea with most of the outbreak centered in and around the city of Daegu, the country’s fourth-largest city with 2.5 million people.

Fifty-three new cases were confirmed, spiking the total to 104 infected as of Thursday evening local time. The number of cases are expected to increase in the coming days.

South Korea also reported its first death, a man in his early 60s, who died at a hospital in Cheongdo, 19 miles south of Daegu. The patient posthumously tested positive after being hospitalized for schizophrenia and later had suffered symptoms of pneumonia, according to the Korea Centers for Disease Control and Prevention.

Health authorities are tracing and testing 1,001 followers at the Shincheonji Church of Jesus in Daegu, since most of the newly confirmed patients attended the church’s services on Feb. 9 and 16. The church has closed all of its 74 branches nationwide and asked followers to access online worship services.

Daegu Mayor Kwon Young-jin urged citizens to refrain from going outside and wear masks, even when indoors.

"National quarantine efforts that are currently focused on blocking the inflow of the virus and stemming its spread are inadequate for preventing the illness from circulating in local communities," Kwon said in a televised news conference.

ABC News' Hakyung Kate Lee and Heejin Kang contributed to this report.