The mishap took place around 7:45 pm on Thursday when the engine of the Barauni Gwalior Mail caught fire and the driver applied emergency brakes causing derailment of seven rear coaches of the train, East Central Railway CPRO Dilip Kumar said.
One of these seven coaches crossed over the down line and was hit by the engine of the Gangasagar Express which was coming on that line between Samastipur and Ujiarpur stations in Barauni section.
There were not many passengers in both the trains and the Gangasagar Express was moving at a slow speed, the CPRO said.
Fire tenders soon reached the spot and doused the fire.
The seriously injured passengers have been identified as Md Rashid Ali and Pramod Kumar. Six others injured are Manohar Ram (driver) of Ganga Sagar Express (Jainagar to Sealdah), Banwarilal Jha (Munger), Nityanad Jha, Manohar Kumar, Yogendra Prasad Singh and Monu, Kumar said.
All the injured were admitted to Railway hospital at Samastipur under Samastipur division of the East Central Railway, he said.
Eyewitnesses said at least 13 passengers were injured and since all of them were locals, they went to nearby private nursing homes and hospitals.
A special train with doctors was sent and the passengers of the two trains were brought to Samastipur for their onward journey.
Efforts were on to clear the tracks to resume normal traffic, Kumar said, adding rail traffic in Barauni-Samastipur section was badly hit because of the accident.
