A Run on Canned Mackerel and Emergency Radios. The Reason? Drones.

One night last week, Henrik Abildgaard, a Danish photographer, stepped out on his porch to have a smoke. He lives in Vestbjerg, a little town in northern Denmark near a military base.

While he was enjoying his cigarette, he said, he saw “something whizzing across the sky and flashing red and green.” A half-hour later, he spotted another one.

What he was witnessing, he soon realized after comparing the video he shot with footage broadcast on TV, was one of the mysterious drone flights that have rattled Denmark in the past 10 days. Several large drones have appeared over military bases and some of Denmark’s biggest airports, including Copenhagen’s, only then to vanish into the night sky.

Analysts suspect, and authorities have implied, that Russia is behind the overflights, as part of a strategy to probe Europe’s preparedness, sow division and unsettle the public.

The last part, at least, seems to be working. Leaders from the 27-nation European Union met on Wednesday in Copenhagen amid greater security than usual to discuss defense and the war in Ukraine. The public anxiety in Denmark over the drone incursions shows how the zone of concern over Russia is steadily growing and how a conflict that once felt far away all of a sudden can feel close.

“We’ve seen a crazy increase in sales,” said Valdemar Badsted, a salesperson at Wolf Tactical, a military surplus shop in Copenhagen. “People are getting worried about war.”

At Wolf Tactical, sales of freeze-dried camping food has shot up by 400 percent, its owner said. Danish news outlets have reported that at other stores, there’s been a run on emergency rations, emergency radios, rice and canned mackerel, too. The Danish public broadcaster just put out a story, “How to talk to your child about drones and hybrid attacks.”

And Denmark’s not alone. Since Sept. 22, Norwegian authorities detected unknown drones in their airspace, too, and briefly shut down Oslo airport. The police in Sweden are investigating reports of drones buzzing a Swedish naval base.

Denmark would be another logical place for Russia to antagonize, analysts say. It has been one of most critical European voices against Russia and one of Ukraine’s strongest supporters; it’s a founding member of NATO; and its defenses are weak.

Peter Viggo Jakobsen, a professor at the Royal Danish Defense College, drew comparisons to Theodore Roosevelt’s old maxim on diplomacy: Speak softly and carry a big stick.

“Denmark has been doing the opposite,” Mr. Jakobsen said. “Denmark is screaming its head off — and we don’t have any stick.”

The government of Mette Frederiksen, Denmark’s prime minister, has boosted military spending, including on long-range precision weapons. Still, many Danes feel their country hasn’t taken its defense seriously enough.

“We’ve been able to just put on an answering machine that says, ‘We’re on a break, just come on in,’” said Mr. Abildgaard, who spotted the drones whizzing around last week.

He considered it “absurd” that a team of crack drone experts from Ukraine, which is fighting a real drone war against Russia, had to come to Denmark to offer help — when normally it is Europe helping Ukraine.

Ms. Frederiksen implied Russia was behind the incursion but wouldn’t quite come out and say it.

“Our authorities haven’t concluded on that question, but when I look at what’s going on around Europe, I don’t think we can see this situation in Denmark disconnected from that,” Ms. Fredericksen said in an interview. “And unfortunately, Russia plays a very negative destructive role.”

How to address this is bedeviling not only her, but other European leaders, who say they want to build a “drone wall” of overlapping radar stations and air defense units.

But drones fall into an airspace gray zone. Military detection systems are built for bigger objects like jets or missiles. Civilian airports mainly monitor airplane traffic. And police forces are not equipped for drone threats.

“That makes this such a scary question,” said Katja Bego, a security analyst at Chatham House in London. “It’s quite accessible technology and it’s pretty hard to stop.”

Marc Santora, Andrew Kramer and Nastya Kuznietsova contributed reporting from Kyiv, Ukraine. Christina Anderson contributed reporting from Stockholm. Henrik Libell contributed reporting from Oslo, Jeanna Smialek contributed reporting from Brussels and Johanna Lemola contributed reporting from Helsinki, Finland.