Lightning struck two homes near Kassel, a duplex in Immenhausen and another home in Bad Emstal-Sand – igniting all four roofs in flames.
Police reported that none of the 12 residents present were injured, but combined damages were estimated at more than €100,000.
The Frankfurt fire department fielded about 90 emergency calls overnight, spokesperson Hans-Jürgen Kohnert said. Most of their operations included pumping out flooded cellars, streets, and underpasses, he said.
Water in some parts of the city reportedly reached 1.5 metres, with the most heavily affected areas in the southern and southwestern city districts.
Meanwhile a Preungesheim-district corrugated iron warehouse roof collapsed under the weight of the heavy rain.
The neighbouring state of Thuringia was also hard hit, as downed trees blocked several roads in Eichsfeld county. Hail the size of tennis balls fell in the region between Bernterode and Martinfeld and lightning set a house on fire in Mühlhausen. Damages were estimated at €50,000.
Violent thunderstorms also rolled over Rhineland-Palatinate between Oppenheim and Worms. Uprooted trees smashed cars and closed roads in the state. Three firemen suffered minor injures.