Unlike the second-home-owning class, many Europeans face the likelihood of spending weeks in quarantine in cramped spaces. Some have been laid off while others must continue to work, sometimes with limited protection, in low-paying jobs like supermarket cashier or delivery that require contact with people.

At first, the French government urged citizens to work from home in order to slow the spread of the virus. But faced with the prospect of people refusing to work because of the health risks, Bruno Le Maire, the finance minister, urged all employees from “activities that are essential to the functioning of the country to go to their workplaces.”

According to both locals and Parisians on the island, some urbanites arrived in Noirmoutier and headed straight to the beach. They were seen picnicking, kite surfing, jogging and biking. In retribution, tires of about half a dozen cars with Paris plates were slashed.

“Their behavior was unacceptable,’’ said Frédéric Boucard, 47, an oyster farmer. “It’s as if they were on vacation.”

Another local, Claude Gouraud, 55, said, “We should have blocked the bridge weeks ago.”

In Italy, currently the European nation with the most infections and deaths, many fled south from the hard-hit north, the region first put in lockdown. Though hard figures are unavailable, some officials in the south have attributed new infections to the influx. Last week, Ruggero Razza, the Sicilian regional council member for health, said on television that many of the new infections in Sicily — which totaled 846 as of Tuesday — had been caused by an influx of nearly 40,000 people from other regions.

In Spain, José María Aznar, the former prime minister, packed his bags for his holiday villa in Marbella, a celebrity resort on the Mediterranean, leaving Madrid on the very day that the capital shut all schools and universities. The move fueled anger across social media as well as calls to monitor Mr. Aznar and lock him inside his villa.