Six persons were killed and several others were injured in a chemical tank blast in Bijnore district of Uttar Pradesh on Wednesday, police said.The incident took place at the Mohit Chemical and Metro factory situated on the Dehat Marg in the morning.Senior officials including the district magistrate Atal Rai and Superintendent of Police (SP) Umesh Kumar Singh rushed to the scene of the incident and are overseeing the relief and rescue operations, a home department officials informed IANS. One labourer is missing.Workers at the factory allege that the chemical tank had been leaking for past many days but despite their please the management turned a blind eye. The incident happened at a time when the labourers were working to plug the leakage by welding it.Those who were killed, are all laborers and have been identified as Chetram, Vikrant, Lokendra, Kamalveer, Balgovind and Ravi. More details on the missing are awaited, an official said.