All arrivals from the United States are to be tested for the new coronavirus within three days of self-isolation, starting Monday, health authorities said.

The strengthened measure against COVID-19 began midnight, according to the Korea Centers for Disease Control and Prevention (KCDC).

It comes as confirmed cases from the US have been increasing steadily despite a gradual decline in domestic cases.

KCDC data showed that 228, or 49.7 percent, out of a total of 459 imported cases came from the US over the past two weeks.

On Sunday, the number of imported cases was 24, with 18 of them coming from the US, followed by Europe with two.

Since March 27, all entrants from the United States have been subjected to strengthened quarantine measures as South Korea grapples with a surge in imported cases of the new coronavirus.

Passengers from the US who do not show symptoms of COVID-19, such as a fever, are required to self-isolate at home for two weeks. Those who show symptoms are required to undergo tests upon arrival.

The country has also been enforcing two-week quarantine and virus tests for all long-term arrivals from Europe, regardless of symptoms.

The country's new virus cases stayed around 30 for the third straight day Monday on the back of a social distancing drive and enhanced quarantine measures.

The country reported 25 more cases of COVID-19, bringing the nation's total infections to 10,537. Of the newly added infections, 16 cases came from overseas. (Yonhap)