Nine inmates at a Seoul prison have tested positive for the coronavirus, all of whom worked in the kitchen, the justice ministry said Tuesday.

The Nambu Correctional Institution in southwestern Seoul conducted COVID-19 tests on dozens of inmates and staff after one prisoner who worked in the kitchen recently showed signs of fever and subsequently tested positive.

The ministry said a total of nine inmates who worked in the kitchen were found to have contracted the virus, leading officials to isolate those who came into close contact in single-person rooms.

The ministry also conducted mass testing on all inmates and staff at the facility, the results of which are expected Wednesday.

More than 40 inmates were transferred to the Yeongwol Correctional Institution in the county some 200 kilometers southeast of Seoul to stop the virus from spreading further.

The confirmation brought the number of the nation's prison-related COVID-19 infections to 1,274 as of 5 p.m., including more than 1,210 cases traced to Dongbu Detention Center in eastern Seoul.

The country added 336 more COVID-19 cases on Tuesday, raising the total caseload to 78,844, according to the Korea Disease Control and Prevention Agency.

The number has stayed in the 300s for three straight days amid the extension of tough virus restrictions and a continued rise in cluster infections. (Yonhap)