Parts of DeKalb County including east and central portions of the county are under a tornado warning until 10 p.m., the National Weather Service issued Sunday.
Severe thunderstorms capable of producing both tornadoes and extensive wind damage were located along a line of storms from Sycamore to near Cortland, moving east at 35 mph, according to the National Weather Service.
Residents are urged to take shelter immediately. Flying debris also could be a risk, and damage to roofs, windows, vehicles and trees is likely, the NWS said.
A flash flood warning also was issued around 9:35 p.m. for DeKalb, Sycamore and Sandwich until 1:30 a.m. Monday.
Nearby Kane County also is impacted, including the areas of Maple Park, Campton Hills, Elburn, St. Charles and Lilly Lake.
A flood watch remains in effect until 4 a.m. Monday, and a severe thunderstorm watch until 1 a.m. Monday.