The mishap occurred last evening when the jeep carrying 13 members of a marriage party was hit by a goods train while it was trying to cross an unmanned crossing at Gobrahi-Rajghat between Majhaulia and Sugauli railway stations, Superintendent of Police (SP) Saurabh Kumar said.
While four occupants died on the spot, seven others succumbed to injuries in hospital, he said, adding the bodies have been sent for post-mortem.
The ill-fated vehicle was carrying members of a marriage party, including the groom and his close relatives, from Babutola to Sugauli (East Champaran), he said.
Meanwhile, the East Central Railway (ECR) DRM Arun Malik visited the spot and ordered manning of the railway crossing there, the SP said.
In Patna, Chief Minister Jitan Ram Manjhi expressed grief over the incident and directed the district administration to undertake rescue and relief works.
He has also appealed to road users to be careful while passing through unmanned crossing.