Over 100 people were killed in an explosion at an industrial gas plant in Nigeria, the media reported on Friday.A truck exploded as it off-loaded butane cooking gas in the town of Nnewi in Anambra state, Xinhua reported.The victims were locals who had come to fill up their gas cylinders and passersby.The dead and injured were taken to the Nnamdi Azikiwe University Teaching Hospital in Nnewi.A witness told the Vanguard newspaper that the blast was triggered when a truck began discharging cooking gas without waiting for the mandatory cooling time.Witnesses say the explosion caused a huge fire that firefighters and residents took several hours to put out.