Four South Koreans working at a US military base in Pyeongtaek, south of Seoul, have tested positive for the new coronavirus, US Forces Korea (USFK) said Thursday.

Two of them last visited Camp Humphreys on Friday and tested positive Tuesday, while the two others were last on the installation Tuesday and were confirmed to have contracted COVID-19 the following day, according to the USFK.

Of the four, three were contractors working together. One of them first tested positive and was transferred to a local hospital, and the two others were confirmed to have contracted the virus in subsequent tests.

The other confirmed patient, a civilian employee, tested positive following a direct contact with an individual who had tested positive for the virus, USFK said.

Except for one of the contractors who has been transferred to the hospital, the other three are waiting to be transported to a medical facility designated for confirmed virus patients, the US military said.

"KDCA and USFK health professionals are actively conducting contact tracing to determine whether anyone else may have been exposed to these individuals and to identify and ensure all known on-post and off-post facilities visited by these individuals are thoroughly cleaned," it said in a release. KDCA stands for the Korea Disease Control and Prevention Agency.

Amid a series of virus cases reported on the base, all non-mission critical work force personnel at Camp Humphreys were temporarily released from duty as of Wednesday afternoon, it said. (Yonhap)