(CNN) — A South Dakota hospital was evacuated after a tornado hit Sioux Falls on Tuesday night, leaving some buildings in shreds.
It’s unclear how many people will be affected by the evacuation at Avera Behavioral Health Center, which suffered storm damage, Mayor Paul TenHaken said. There have been no reports of casualties, but the 911 system is backed up, he added.
The National Weather Service confirmed a tornado on the south side of the city. Nearly 18,000 customers were without power Wednesday morning, according to utility company Xcel Energy.
Sioux Falls Police warned people to stay off the roads due to downed power lines and trees. Most of the damage is in the south and southeast part of the city, the mayor said.
Please stay off the roads — there’s a lot of people that either is still on the roads who didn’t get off in time for the storm or are back on to see the damage,” he said in a video message.
“You need to stay off the roads. There are severe power outages throughout the city,” he said.
The tornado struck as strong thunderstorms and flash flooding rolled through the area. “A very dangerous storm moving int the Sioux Falls area! Winds of 90 mph possible. Take cover!” the NWS tweeted.