Prime Minister Mette Frederiksen said Wednesday the decision had been made with a "heavy heart," but it was necessary based on the recommendation of health authorities.

"The virus has mutated in mink. The mutated virus has spread to humans," Frederiksen said.

Statens Serum Institut, the Danish authority based in Copenhagen which deals with infectious diseases, had found five cases of the virus in mink farms and 12 examples in humans that showed reduced sensitivity to antibodies, she said. Allowing the virus to spread could potentially limit the effectiveness of future vaccines.

"We have a great responsibility towards our own population, but with the mutation that has now been found, we have an even greater responsibility for the rest of the world as well," Frederiksen said.