Officials in the Swiss mountain resort of St Moritz quarantined employees and guests of two luxury hotels, closed ski schools and kept schoolchildren home from class on Monday after a dozen positive tests for a highly infectious coronavirus variant, Reuters reports.

About 300 employees and 95 guests at the Grand Hotel des Bains Kempinski St Moritz and Badrutt’s Palace Hotel were quarantined. The eastern canton of Grisons ordered everyone to wear masks in the town of 5,200 that prides itself as a birthplace of modern winter sports.

Those under quarantine will be tested and those receiving positive tests isolated. Those who test negative may be able to depart, a spokesman for the region’s coronavirus task force said, but must follow quarantine rules once they arrive home.

The nationalities of those affected were not given, but Grisons said foreigners were likely among hotel guests.