A powerful blast at an explosives factory in the Czech Republic has left four people missing and at least seven injured. The blast took place Wednesday morning at the Explosive factory in the central Pardubice region, destroying one building and shattering windows in a four kilometer area around the factory. The blast was believed to have been triggered by nitroglycerine. The factory produces a variety of explosives for commercial and military applications. Rescue workers with sniffer dogs were trying to locate the missing victims.