SEOUL: South Korea reported 505 additional COVID-19 infections in its largest daily increase on Thursday (Feb 27), as the United States issued a new warning against travel to the Asian nation.
Both US and South Korean forces also postponed a joint drill.
The new cases take total infections to 1,766, the Korea Centers for Disease Control & Prevention (KCDC) said, the largest daily jump since the first confirmed infection on Jan 20.
South Korea also reported a 13th death.
Of the new cases, 422 were in the southeastern city of Daegu, the location of a church at the centre of South Korea's outbreak, the KCDC said in a statement.
READ: More COVID-19 new infections outside China than inside: WHO
The US State Department raised its travel advisory level, urging citizens to "reconsider travel" to South Korea.
In Seoul, the capital, people waited in long queues at some stores to buy masks, which have been in short supply, despite only a few dozen infections reported in the city.
The past week's sudden surge in cases has ignited criticism of the government's handling of the crisis, particularly a decision to limit arrivals from China, rather than imposing a blanket ban.
Feelings on the issue run so high that more than 1 million people have signed a petition demanding the impeachment of President Moon Jae-in.
The coronavirus that can lead to pneumonia is believed to have originated in the central Chinese city of Wuhan late last year before killing more than 2,700 and infecting about 80,000, the vast majority in China.
US-SOUTH KOREA JOINT MILITARY EXERCISES POSTPONED
The US military reported its first novel coronavirus case on Wednesday, in a 23-year-old soldier based in Camp Carroll, about 20km from Daegu.
About 28,500 US troops are stationed in South Korea, which remains technically at war with North Korea.
The South Korean military has also reported at least 21 infections, and has confined most troops to their bases.
Forthcoming joint military exercises between South Korea and the US have been postponed over the outbreak, the two countries announced on Thursday.
The decision was made after Seoul declared its highest "severe" alert level over the virus, Combined Forces Command said in a statement, adding the combined command post-training had been postponed "until further notice".
The US commander in South Korea agreed to the delay after a request by the chairman of its joint chiefs of staff.
READ: Shincheonji - The secretive sect in South Korea's COVID-19 outbreak
The security allies have previously scaled back their annual joint military exercises significantly to facilitate nuclear talks with Pyongyang - which condemns such drills as preparations for an invasion - but a command coordination exercise had been planned for this spring.
On Thursday, media said a Korean Air flight attendant who tested positive for the virus had worked on flights between Seoul and Los Angeles.
The attendant had been on a Korean Air KE958 flight from Israel to Incheon on Feb 15 and Feb 16, the KCDC has said. Passengers included a South Korea tour group among whom 31 virus cases were seen to have originated.
The agency has not released details of other routes and flights flown by the employee.
Yonhap News Agency and other media said she worked on flights KE017 and KE012 on Feb 19 and Feb 20 to and from Los Angeles. About 30 crew on the same flights are in self-quarantine for 14 days, media added.
The US may in future have to curb travel to Italy, South Korea and other countries over the virus, President Donald Trump said on Wednesday, but now was not the right time, he added.
South Korea has the most virus cases outside China and Italy and Iran are emerging as new epicentres of the rapidly spreading illness.