The Amritsar-Katihar Amrapali Express moving at slow speed hit an engine going to yard following which three bogies of the Express train derailed and hit a pillar of the overbridge, Chief Public Relations Officer (CPRO), East Central Railway (ECR) Amitabh Prabhakar told PTI.
The foot over bridge was not in use, the CPRO said.
He said there was no report of any casualty.
But, up and down line at Samastipur were closed after the incident and would be restored only after clearance of debris.
Divisional Railway Manager (DRM) Samastipur Arun Mallik said the incident would be probed.
The caving in of overbridge at Samastipur came close on heels of similar incident at Muzaffarpur in November last year.