An explosion at an illegal firecracker unit located at Egra in Purba Medinipur district of West Bengal killed nine people and injured several others on Tuesday, a senior police officer said. The impact of the explosion was so massive that the factory which was being run from a residential building collapsed. While the state government ordered a CID probe into the incident, the opposition BJP demanded an investigation by the NIA and wrote a letter to Union Home Minister Amit Shah in this regard.