Shoppers are buying six-month food supplies wrapped in military-grade Mylar pouches, and kits filled with duct tape, food bars and an air-filtration mask.

Some companies that specialize in selling items to people planning for the worst — so-called doomsday preppers — say they have had a bump in sales this week, after tensions rose between the United States and North Korea. Online searches for prepping and survival gear have also jumped.

The increase in sales is a turnaround from recent months. Revenue fell after Mr. Trump’s election, according to three of the country’s larger retailers that specialize in selling emergency preparedness.

“The whole industry kind of took a little pause after the election of Trump,” said Brandon J. Garrett, director of marketing at The Ready Store, which sells a wide range of prep products online and via catalog. “I think everyone was kind of waiting to see what kind of leader he was going to be and where he would take the country.”

“This week, it kind of seemed that everything picked up,” he said.

Emergency gear has its own retail niche, with devotees attending conventions and manufacturers coming up with specialty products. Some in the industry trace its rise to the aftermath of the Hurricane Katrina disaster in New Orleans; others believe it was stoked by those who opposed President Barack Obama’s two terms.

Prepper companies sell a wide variety of wares, from 41-pound pails of pinto beans and freeze-dried roasted chicken to fire-starter devices and water filters. Like other retailers, the companies have set up online sites, complete with one-day sales and discount codes. There are also traditional retail emergency readiness stores around the country.

Emergency Essentials operates four retail stores in Utah. The stores, in or near strip malls in towns outside of Salt Lake City, look a little like Petco, but the aisles are filled with ready-to-eat meals and solar generators instead of bags of kibble and litter.

The company got its start almost 30 years ago selling to members of the Church of Jesus Christ of Latter-day Saints — the church stresses preparedness — but has expanded its business to serve a wider audience across the country, according to Kevan Allbee, a marketing manager for Emergency Essentials.

When Mr. Trump won, “sales started a downward decline,” Mr. Allbee said. “In short summary, what we understand is when the left is in power, the right panics.”

Shane Sullivan, the company’s president, said that sales at Emergency Essentials on Tuesday, after President Trump made comments to reporters about North Korea, were double their usual amount. And revenue on Wednesday and Thursday surpassed what came in Tuesday.

Clockwise from top left: a radio and cellphone charger; a portable toilet; a grill that runs on propane, charcoal or wood; generators and solar panels. CreditDerek Israelsen for The New York Times

“Clearly, when something happens in the world like North Korea right now, it is on people’s minds,” Mr. Sullivan said. “It just causes them to rethink where they stand in the event of war, in the event of job loss, in the event of a natural disaster.”

Not every company in the prepper industry has seen an uptick. Joe Marshall, managing editor of Survival Life, a website that supports an online retail operation and the Banana Bay Tactical shop in Austin, Tex., said it was too soon to see an impact on sales.

“The truth is, there’s been some chatter,” he said, “but for most of our people, they’re already preparing.”

Google searches for “prepper” hit their highest level in a month on Tuesday, while searches for “survivalism” neared a high last reached in July, according to Google Trends, a site from the technology giant that shows what users have been researching.

Keith Bansemer, vice president for marketing at My Patriot Supply, which sells bulk food, water devices and seeds, said customers have started snapping up the company’s six-month food supplies. They wanted to do something to feel more secure, he explained.

By prepping, “you’re actually alleviating fear,” Mr. Bansemer said.