Denmark on Friday defended the strict measures it has imposed on the north of the country after a mutated version of the new coronavirus linked to mink farms was found in humans.

Copenhagen has warned that the mutation could threaten the effectiveness of any future vaccine, and has ordered the slaughter of all of the country's minks, estimated at up to 17 million.

"These are timely and necessary measures" amid a "worrying" development, Foreign Minister Jeppe Kofod said at a press conference for foreign press.

The Scandinavian country on Wednesday announced the mutation had jumped from minks to humans and infected 12 people.

Those cases were all detected in the North Jutland region, officials said Friday, correcting earlier information that the region was home to 11 of the 12 cases.

In seven North Jutland municipalities, the estimated 280,000 residents were on Thursday urged to stay within their municipal borders to limit the spread of infection.

Public transport in the region has been halted and bars and restaurants ordered shut, and some schoolchildren will also have classes online in restrictions that are due to last a month.

Scientists say virus mutations are common and often harmless, and this one doesn't cause a more severe illness in humans.

Denmark has ordered the slaughter of all of the country's minks, estimated at up to 17 million
Denmark has ordered the slaughter of all of the country's minks, estimated at up to 17 million Ritzau Scanpix / Mads Claus Rasmussen

But Danish health authorities have expressed concern that this strain, known as "Cluster 5", is not inhibited by antibodies to the same degree as the normal virus, which they fear could threaten the efficacy of vaccines that are being developed across the globe.

Scientists around the world have noted that little is known about "Cluster 5", urging Danish authorities to share their research.

In addition, the 12 human cases date back to September with no new cases reported since, raising questions Friday about whether Denmark had overreacted.

"We'd rather take a step too far than a step too little," Kofod told reporters.

Further research on "Cluster 5" is ongoing, Danish officials said.

The Stockholm-based European Centre for Disease Prevention and Control (ECDC) said Friday it was "in close contact" with Danish health authorities on the issue.

"The possibility of an antigenic mutation in SARS-CoV-2 may have potential implications for immunity, reinfections and the effectiveness of COVID-19 vaccines, but there is currently high uncertainty. Further analyses and scientific studies are needed to better understand the identified mutations and their potential implications," it said.

On Friday, more than 100 mink farmers protested against the mink slaughter, which is due to be completed in a few weeks.