A tornado tore through northeastern Wisconsin on Monday, part of a system of severe storms that knocked out power to tens of thousands of residents, downed trees, leveled buildings, ripped roofs off homes and shut down at least one city as it tried to emerge from the damage.

Mayor Austin Hammond of Menasha declared a local state of disaster on Monday, saying in a news release that the city was closed. The City of Menasha Police Department said traffic into Menasha was temporarily suspended as crews cleaned up roadways for emergency and essential vehicles and warned drivers not to try to drive into the city’s limits. Downed power lines and debris devastated the area, and at least one emergency shelter was open for affected residents.

According to the National Weather Service, radar confirmed a tornado hit Winnebago County just before 1 p.m. local time. Residents were urged to take cover. There were no immediate reports of fatalities or injuries. Drone footage shown by TMJ4, an NBC News affiliate, showed buildings and homes in Menasha that were badly damaged or destroyed.

Gordon Hintz, the top elected official in Winnebago County, Wis., told The A.P. he was not aware of any deaths or injuries, but the authorities were watching for that possibility. “Obviously, the footage looks devastating,” Mr. Hintz said. “Clearly some significant damage done with power lines down and things like that.” He also told The A.P. he had heard reports of destroyed buildings.

The storms were expected to last into the evening.

Tom Nelson, the county executive for Outagamie County, which includes Appleton, Wis., told The Associated Press that “all indications are that this was a devastating system that has caused extensive damage.”