Powerful thunderstorms including a tornado unleashed heavy rain and strong winds across the Upper Midwest region on Monday, knocking out power to thousands of customers, downing trees, damaging buildings and making some roads impassable.

More storms were expected into the evening.

At least one tornado was confirmed near Northern Lake Winnebago in Wisconsin.

Mayor Austin Hammond of Menasha declared a local state of disaster on Monday, saying in a news release that the city was closed. Emergency medical workers were working to secure the area, which was hit by downed trees and power lines, Mayor Hammond said. At least one emergency shelter was open for affected residents.

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.” Drone footage shown by TMJ4, an NBC News affiliate, showed buildings and homes in Menasha that were badly damaged or destroyed.

Photos and videos on social media appeared to show buildings damaged in areas around Appleton. The Appleton Police Department said there were several large tree limbs down throughout the city and that it was working with other nearby agencies to “respond to many storm related calls” on Monday afternoon.

By early afternoon, the National Weather Service had already issued multiple tornado warnings as the storms began sweeping through, including at least one described as a “particularly dangerous situation,” the most severe warning.