Berlin, Aug 4 : After an explosion at a police blasting site in Berlin's Grunewald forest, a fire has broken out in the adjacent forest and is spreading, the fire brigade said on Thursday. An area of roughly 1.5 hectares was affected and further explosions have occurred, reports dpa news agency. Residential areas are not in danger, however, according to firefighters. "We will prevent that," a spokesman said. Though there have been no casualties, Berliners are being told to avoid the area as far as possible. It is assumed that the extreme dryness in the area will influence the further course of the fire. The extreme heat expected on Thursday will be especially hard on the emergency services. Due to further explosions and flying debris, the fire brigade said it had not yet started extinguishing the fire, and the emergency services had initially withdrawn to about 1,000 metres away. There are 100 firefighters and police at the scene. Additional firefighters and special forces from the Bundeswehr have been requested. Water cannon and evacuation tanks have also arrived. According to a police spokesperson, it is still completely unclear how the explosion could have occurred. The site is used to dispose of ammunition in a controlled manner. /IANS