The rise in cases comes as the country tries to put in place a plan for some 900 students due to return from skiing holidays in northern Italy.

The group, members of a fraternity in the northern Dutch city of Groningen, travelled to Sestriere in the Italian Alps before the Dutch government changed its travel advice to say all trip to the region should be cancelled unless necessary.

However, Hanneke Mensink, the local health authorities' spokeswoman, told Reuters they had been warned before they left at the weekend.

"We told them our worries, but they decided to go anyway. That is their responsibility."