Health authorities reported 52 new cases of the illness, raising South Korea's total to 156, most of them since Wednesday. The spike, especially in and around Daegu, has raised fears the outbreak is getting out of control in the country.
In the capital, Seoul, officials banned major downtown rallies to try to fight the outbreak.
And the first two cases were confirmed in South Korea's 600,000-member military, a navy sailor and an army officer who had both visited Daegu recently.
Prime Minister Chung Se-kyun said in a televised statement the central government will concentrate its support to the southeastern region to ease a shortage in sickbeds, medical personnel and equipment.
"A month into the (COVID-19) outbreak, we have entered an emergency phase," Chung said. "Our efforts until now had been focused on blocking the illness from entering the country. But we will now shift the focus on preventing the illness from spreading further in local communities."
The surge of infections in Daegu and several cases in Seoul with unclear infection routes forced government officials to acknowledge Thursday for the first time that the virus was circulating in the local population.
Initial cases of the illness in South Korea had been connected to China, where the illness has sickened tens of thousands of people and caused more than 2,200 deaths. One death has been reported in South Korea.
Daegu Mayor Kwon Young-jin on Thursday urged the city's 2.5 million people to stay home and wear masks even indoors if possible.
Officials on Jeju Island said a 22-year-old navy sailor based on the island tested positive for the virus on Friday, days after visiting Daegu for a vacation. The sailor currently hospitalized at a civilian hospital on the island is Jeju's first virus patient. The Jeju provincial office said in a statement said officials convened an emergency meeting Friday to discuss how to prevent the spread of the disease.
The Defense Ministry said the sailor is also the first virus case in South Korea's military. South Korea has about 600,000 troops, 70,000 of them navy sailors or marines, according to the ministry.
Later Friday, North Chungcheong Province governor Lee Si-jong told reporters that an army officer based in the central province also tested positive for the virus. He also visited Daegu recently, according to province officials.
Most of the new cases in the southeastern region are linked to a church in Daegu.
The Shincheonji church, which claims about 200,000 followers in South Korea, said it has closed all of its 74 sanctuaries around the nation and told followers to instead watch its worship services on YouTube. It said in a statement that health officials were disinfecting its church in Daegu and were tracing the woman's contacts. The Daegu church has about 8,000 followers.
The World Health Organization said the jump in cases in South Korea doesn't signal an increased risk of a global pandemic. WHO Director-General Tedros Adhanom Ghebreyesus said the new cases were mostly linked to known, existing clusters of infections and that South Korean authorities were following them very closely.
"The number of cases are really manageable, and I hope South Korea will do everything to contain this outbreak at this early stage," he said.
He noted that more than half of the COVID-19 cases outside China are from Diamond Prince cruise ship docked in Japan.