A strong storm system coming out of the Great Plains brought severe thunderstorms to the Midwest on Thursday, including a reported tornado that swept through a small Wisconsin city, damaging businesses and homes, forcing road closures and downing power lines, the authorities said.

Rob Boelk, the mayor of Mayville, Wis., a city of about 5,100 residents, said no serious injuries had been reported and that the authorities were still assessing the damage.

“The whole south end of town has been hit pretty hard,” Mr. Boelk said in an interview, adding that about 100 workers at a manufacturing center there had to be moved to a safer area.

The Dodge County Sheriff’s Office said there was also significant damage in Juneau, Wis., a nearby small city of about 2,500 residents, and instructed people to stay away from damaged areas. Emergency crews were helping to clear obstructed roads and to fix power outages, the office said on social media.

As of 9 p.m. Eastern time, more than 60,000 customers in Wisconsin were without power, according to Poweroutage.us, which tracks outages nationwide.

In western Wisconsin, at least several tornadoes were reported in the areas of New Richmond and Hammond, which are in the Minneapolis metro area. The St. Croix County Sheriff’s Office reported some property damage and no injuries.

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