European industry thrived for decades on a steady supply of cheap Russian gas, which flowed uninterrupted throughout the Cold War and other times of tension between Moscow and the West.

Since invading Ukraine, Russian President Vladimir Putin has weaponized the country’s vast stores of energy to undermine support for Kyiv. He turned off the taps to the biggest natural-gas pipeline, Nord Stream, completely this month.

The impact has pushed Europe to the brink of recession and threatens to inflict lasting harm on its manufacturing businesses. Unlike the U.S., Europe leaned on manufacturing and heavy industry to keep its economy chugging in recent decades. A bigger chunk of its economy comes from the likes of steelmakers, chemicals producers and car makers.

Europe’s energy crisis has left few businesses untouched, from steel and aluminum to cars, glass, ceramics, sugar and toilet-paper makers. Some industries, such as the energy-intensive metals sector, are shutting factories that analysts and executives say might never reopen, imperiling thousands of jobs.

The question is whether the current pain is temporary, or marks the start of a new era of deindustrialization in Europe. The bloc has scoured the world for alternative gas supplies, striking deals to buy gas from the U.S., Qatar and elsewhere. But the continent might never again have access to the cheap Russian gas that helped it compete with the resource-rich U.S. and offset high labor costs, rigid employment rules and stringent environmental regulations.

In the city of Žiar nad Hronom, Slovakia, built around a 70-year-old aluminum factory that supplies car-part makers across the continent, some fear for their financial future. “This is probably the end of metal production in Europe,” said Milan Veselý, who has worked at Slovalco, majority owned by Norway’s Norsk Hydro AS A, all his adult life, following in his parents’ footsteps.

Slovalco is among the companies hit by volatility in electricity prices across Europe caused by low Russian supplies of power-generating gas. For years the factory was by far the biggest buyer of power in Slovakia, consuming 9% of the country’s electricity, most of it from nuclear energy. Before energy prices started rising last year, Slovalco paid about €45 (about $45) for each megawatt-hour of power. In 2022 so far it has paid €75, in a deal locked in last year. In late August, prices hit €1,000 across Europe.

Slovalco didn’t renew its power contract for 2023, which would have cost €2.5 billion euros at the recent peak in power markets. Mr. Veselý, the plant’s manager, is winding down primary-metals production, leaving a small recycling operation. He is also dismissing 300 of 450 workers. “The volatility of the price of electricity these days—it’s crazy,” he said. “This is the way we are actually killing industry.”

Factory curtailments and closures have saved fuel in Europe’s quest to reduce demand. Along with the hunt for non-Russian supplies, that’s enabled the European Union to sock away enough gas to fill over 80% of its storage capacity, probably enough to get to spring without government-enforced quotas even if Mr. Putin cuts supplies to zero, analysts say.

The judgment most governments have made is that slowing and shutting factories now is preferable to cutting off power to hospitals and schools over winter. Europe consumed 10% less gas than the average for the time of year in August, according to commodities-data firm ICIS. The EU is aiming for demand reductions of 15%.

The factory closures come at a ruinous cost. Companies in energy-intensive industries say they face going bust this winter without government support. Complex supply chains in sectors such as the auto and food industries are getting gummed up, adding to inflationary pressures just as pandemic snarl-ups show signs of easing.

Norwegian fertilizer giant Yara International AS A, which uses gas as an ingredient, has cut crop-boosting ammonia production by 65% across its European factories.

“We think about things we wouldn’t dare to think about a year ago,” said Michael Schlaug, general director of Yara’s Sluiskil facility in the Netherlands, which stopped the second of three ammonia plants in late August. Engineers are rejigging machinery to accommodate imported ammonia with higher water content as the facility turns to shipments from the U.S., Trinidad and elsewhere to replace products it previously made.

Dutch fertilizer company OCI NV is importing more ammonia through Rotterdam. It plans to triple its capacity at the port by next year and is expanding its Beaumont, Texas, facility to produce ammonia that can be transported to Europe and Asia.

“It really tips the scales in the U.S.’s favor,” Chief Executive Ahmed El-Hoshy said of energy costs.

A reduction of Europe’s industrial capacity would deepen the reliance on materials and parts made overseas at a time when governments are striving to bring supply chains for renewable energy, electric vehicles and military arms closer to home.

Metals producers, which require significant power to break down and form chemical bonds, are at the front of the crisis. Electricity prices have more than doubled this year, propelled by high gas prices, trouble in France’s nuclear fleet of power plants and low hydropower generation.

ArcelorMittal SA, one of the world’s largest steelmakers, will close a blast furnace in Bremen and a so-called direct reduction plant in Hamburg that produces sponge iron, used to create crude steel. In Germany, ArcelorMittal had already reduced gas demand by about 40%, compared with what it planned to consume at the start of the year.

“We have never had such upheavals in the energy prices,” said Reiner Blaschek, chief executive of the company’s German business. “Everything that is associated with enormous volatility in the short term is for us as a commercial enterprise, to put it mildly, pure poison.”

“You have to reinvent the whole energy supply chain on the go,” Mr. Blaschek added.

ArcelorMittal Germany has been buying sponge iron externally from the U.S. instead of making it locally using gas.

Zinc stockpiles have almost run out in the EU, leading customers to import metal from China, according to metals industry lobby group Eurométaux. Analysts say European output of primary aluminum is dying out, leaving the continent with recycling operations that produce metal suitable for industries such as packaging, but not for wheel hubs, brakes or parts for airplanes.

Aluminum smelters are finding themselves not able to renew their power contracts. Companies need 15 megawatt-hours of power to produce a metric ton of primary aluminum, costing €9,000 at recent electricity prices, while a metric ton can be sold for less than €2,500, according to Germany’s metal association, WV Metalle.

“We need immediate emergency aid now, otherwise we are threatened with deindustrialization in Germany,” said Franziska Erdle, WV Metalle’s general manager.

Alcoa Corp.’s San Ciprián aluminum plant in Spain, Glencore PLC’s Portovesme zinc smelter in Italy and Trafigura Group’s zinc factories in the Netherlands, France and Belgium have curbed or closed production. Half of the EU’s aluminum and zinc capacity is offline, on top of curtailments in silicon and alloys of iron, Eurométaux said in a letter to EU officials this month.

Tom Price, head of commodities strategy at Liberum, likens the shock to the surge in energy prices that killed off Japan’s aluminum industry in the 1970s. “This is such a severe event and Europe’s industrial base has become very heavily dependent on Russia for cheap energy inputs,” he said. “It may not be able to come back.”

Lower output from Europe’s factories threatens to cascade through supply chains. Auto makers have been hit both in their own dependence on gas for power and heat and indirectly through supply issues. Volkswagen AG said it has been stockpiling glass products, such as windows and windshields, fearing a shortage of gas could hit glassmakers.

A spokeswoman for Safran SA, a French maker of aircraft engines and defense-related equipment, said a fragile supply chain had limited the company’s ability to raise production. So far it has been able to buy metal from existing suppliers but the company is monitoring the situation, she added.

In food production, sugar factories are powered by natural gas. Germany’s federal competition authority said this month the country’s four producers would be allowed to cooperate if supplies are cut off, for example by making capacity available to each other. If the sugar plants stop, large parts of the beet harvest would likely rot and prices would rise for consumers already dealing with food inflation.

The companies are racing to find alternative energy supplies to maintain the sugar output. Securing them is difficult because it requires new logistics and storage facilities, said Südzucker AG , one of the four companies.

Some factories, such as zinc manufacturers, can restart quickly when the economics add up again. For others, including glass and aluminum makers, reopening is a lengthy and expensive process that may never make financial sense.

Even toilet-paper makers are feeling the crunch. Hakle GmbH, a German toilet-paper and hygiene-product maker this month declared itself insolvent and sought protection from creditors because it could no longer raise prices enough to offset higher paper costs due to energy prices.

At Slovalco in Slovakia, Mr. Veselý sold the electricity the company had bought for the rest of the year, netting €160 million to spend on taxes and a possible restart in the future. Operators set about disconnecting podlike metal cells that turn white alumina powder into molten aluminum in the vast hall that is the factory’s nerve center. The hangar is also the factory’s biggest vulnerability, because the cells depend on a 285,000-amp current.

Ten of the 226 cells remain in action, but are due to wind down by the end of the year. Firing the factory up again would require replacing their electrical connections—a process that would take a year and cost up to €90 million, Mr. Veselý said.

“Everyone is concerned,” said Tomáš Chrien, who has worked at Slovalco since 1993 and is an operator in the building next door, where molten aluminum is fashioned into solid cylinders. Marián Hárezník, a processes expert, said the job brings a good, stable salary and a sense of camaraderie. “No one expected we would be in a situation like this—ever,” he said.

Municipal official Martin Baláž said his big worry is the 2,500 jobs at companies that supply and service Slovalco. At one local firm, Remeslo Strojal, s.r.o., 50 employees whose job was to maintain the factory’s cells are looking for new work, he added.

Branislav Strýček, chief executive of utility Slovenské Elektrárne, A.S., which supplied power to Slovalco, worries many more Slovak firms will shut down because he estimates more than half haven’t procured power for 2023.

“These electricity prices are sick,” he said, adding that he is in the odd position of running a utility and wanting the government and EU to take measures to limit prices. “Your customers will not survive so you’ll have no one to deliver [to].”