Frankfurt (dpa/lhe) - In the Dornbusch district of Frankfurt, the roof structures of two residential buildings burned on Sunday afternoon. It was initially unclear how the fire broke out, the police said on Sunday. Firefighters were able to extinguish the fire by early evening. None of the residents of the semi-detached houses were injured. However, they were unable to return to their living quarters on Sunday. The police are now investigating how the fire could have started. The amount of damage caused by the fire was initially unknown.