SEOUL, South Korea — South Korean health officials say they have detected the first local transmissions of what are feared to be more contagious forms of the coronavirus first identified in Britain and South Africa.

The Korea Disease Control and Prevention Agency said Wednesday said it found four local cases of the British variant and one local case of the South African variant.

Since October, health workers have found 39 cases of new variants of the virus that causes COVID-19, also including a form that was first identified in Brazil. The previous cases were found in people arriving from abroad.

In all five of the locally transmitted cases, the virus carriers had been infected from relatives who recently arrived from abroad, the agency said.

The KDCA said it is expanding contact tracing to determine whether the new variants could have circulated further. It also called for administrative officials to strengthen monitoring of passengers arriving from abroad so that they minimize their contact with other people during their two-week quarantine, which in most cases can be done at home.