Chennai: A 22 year old woman passenger was killed and 11 others were injured when two bombs went off in quick succession in two coaches of the Guwahati-Bangalore Express at the Chennai Central railway station, the main railway hub here. Southern Railway General Manager Rakesh Mishra told reporters that the minor intensity blasts took place in S-4 and S-5 sleeper coaches after the train arrived at the station. Seven persons received minor injuries, Mishra said. The injured were taken to the government-run hospital across the road. Mishra said the police was investigating the nature of the blast and those who could be behind it. Police have mounted a massive search operation in all the trains following the incident.