A building in the center of Madrid, Spain, exploded on the 6th, injuring 18 people and missing 2 others. A spokesman for the Madrid emergency department said that on the afternoon of the 6th local time, an explosion occurred on the top floor of a four storey building in Salamanca District of central Madrid, injuring 18 people, four of whom were sent to hospital for treatment and one was seriously injured. Rescuers are searching for two missing persons. The building was seriously damaged in the explosion, and the surrounding roads and parked vehicles were affected. The cause of the explosion is under investigation. According to Spanish media reports, the explosion may be caused by natural gas leakage or boiler explosion, and the technicians of the natural gas company are testing on site. (Xinhua News Agency)