(Bloomberg) -- Tesla Inc. stopped production at its factory outside of Berlin and sent workers home after suspected arson at a nearby electricity tower caused power failures throughout the region.

Brandenburg police have dispatched helicopters, drones and service dogs to investigate whether the fire in Gosen-Neu Zittau was set intentionally, local authorities said Tuesday. Tesla wasn’t yet able to say when production at its sole European factory can resume.

“We are very concerned about the safety of our employees here,” André Thierig, the plant manager at Tesla’s factory in the small town of Gruenheide, told reporters. The facility currently has a capacity to produce 375,000 cars a year.

Tesla fell as much as 5.2% after the start of regular trading Tuesday in New York, with the production halt as well as disappointment over its China shipments weighing on the shares. They plunged 7.2% on Monday, dropping Chief Executive Officer Elon Musk out of the top spot on the Bloomberg Billionaires Index for the first time in more than nine months.

An organization calling itself Volcano Group claimed responsibility for the fire in a letter posted on an alternative website. “We sabotaged Tesla today,” the group said, without identifying any individual authors or alleged participants in the action.

Tesla’s German factory has long experienced pushback from disgruntled locals and environmental groups. First announced in late 2019, the plant’s opening was delayed for months by legal challenges from groups concerned the site would use too much water and threaten local wildlife. The facility, which makes the Model Y — Europe’s best-selling passenger car last year — employs around 12,000 people.

Activists have been camping in a forest near the plant since last week to protest its potential expansion. They’ve set up tents and built tree houses to stop the carmaker’s plans to raze around 140 soccer fields of wooded area to make way for logistics buildings. On Tuesday, several of them mingled in the wooded area near Tesla’s factory, with one man hanging from a zipline tied between two pine trees.

Some of the activists in the forest are part of a group called “Stop Tesla,” which distanced itself from the fire, saying it didn’t know who or what was responsible, and that it stands in solidarity with the carmakers’ workers and local residents.  

“We use our bodies and tree houses to oppose the expansion of the factory,” the group said Tuesday. “We are not endangering human lives in the process.”

Dietmar Woidke, Brandenburg’s state premier, said the suspected arson would amount to an act of terrorism, and said federal prosecutors would take over the investigation if evidence shows that the fire had been set intentionally. Musk weighed in on the incident with a post on X.

Last month, local residents broadly rejected Tesla’s expansion plans in a non-binding referendum. The carmaker wants to chop down trees to build a freight depot, warehouses and a kindergarten. There also have been reports that the plant has been discharging more hazardous substances into the local waste-water system than allowed.

(Updates with Tesla official’s comment in third paragraph.)

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