The country announced more than 150 cases, many in the densely populated region around Milan, as officials closed schools and canceled Venice’s carnival celebrations.
The worrisome spike — from fewer than five known cases in Italy before Thursday — shattered the sense of safety and distance that much of the continent had felt in recent months even as the virus has infected more than 78,000 worldwide and killed more than 2,400, nearly all in China.
Already, a new nervousness has pervaded Europe.
In Italy’s Lombardy region, 10 towns were locked down after a cluster of cases suddenly emerged in Codogno, southeast of Milan.
Residents were supposed to leave or enter the towns only with special permission, affecting at least 50,000 people, and by Sunday night, police officers in surgical masks were waving down cars.
Austrian officials stopped a train en route from Italy to Austria and Germany to test passengers for the virus. The Austrian interior minister, Karl Nehammer, said the tests came back negative so the train got the “all clear.”
In France, the new health minister, Olivier Veran, stressed the country’s preparedness, saying it would significantly ramp up its testing.
“There is a problematic situation at the door, in Italy, that we are watching with great attention,” he said on Sunday, adding that a Europe-wide discussion between health ministers was in the works.