A couple was arrested for violating coronavirus quarantine, to which they were restricted after at least one of them tested positive for the coronavirus on arrival from South Africa, according to local news reports.

The incident comes as Europe goes on high alert over the appearance of the omicron variant of the coronavirus in at least 12 countries across the continent.

The married couple, a Portuguese woman and a Spanish man, were arrested Sunday evening at Schiphol airport in Amsterdam, moments before their flight was scheduled to depart for Spain. They have since been placed in isolation in a hospital, according to Het Parool, a Dutch newspaper.

The man and woman, whose names were not released, had arrived to the Netherlands on a flight from South Africa, and at least one of them tested positive for the coronavirus after landing at Schiphol airport. They were placed in isolation in a hotel along with travelers from southern Africa.

They left the hotel around 6 p.m. Sunday. Security guards alerted the Marechaussee, a national police force, according to the Guardian. The couple was arrested on the plane “almost silently and without violence,” a Marechaussee spokesman said.

Dutch police did not respond immediately to a request for comment.

The Netherlands has tightened coronavirus restrictions in response to a surge in cases. Recreational venues such as bars, museums, movie theaters and cafes must close by 5 p.m. local time for the next three weeks, according to the Guardian.

Scientists in South Africa confirmed Thursday that they had detected a new variant with a high number of mutations, which raised concern among experts. The World Health Organization dubbed it omicron and designated it “a variant of concern.” A number of countries imposed restrictions on travel from countries in southern Africa.

The omicron variant has been identified in at least 12 countries in Europe: Austria, Belgium, Denmark, England, France, Germany, Italy, the Netherlands, Portugal, Scotland, Spain, Sweden, along with a probable case in Switzerland.

The European Union on Friday announced restrictions on travel from seven countries in southern Africa: Botswana, Eswatini, Lesotho, Mozambique, Namibia, South Africa and Zimbabwe.

British Primer Minister Boris Johnson announced a return, months after it was lifted, to a mask requirement in public settings, such as on public transportation and in stores. Travelers to Britain will be required to take a PCR test on the second day after arrival and to self-isolate until they get a negative result, he said in a news conference Saturday.

“The measures that we’re taking today, including on our borders and on face masks, are temporary and precautionary, and we will review them in three weeks,” he said. “At that point, we should have much greater information about the continuing effectiveness of our vaccines.”

This report has been updated.