The victims, mostly kanwarias (devotees of Lord Shiva) had got down from another train and were walking on the tracks when the mishap took place, official sources said. The devotees were on way to a Shiva temple.
At least 20 of them died on the spot after being run over by the speeding train, they said, adding that the number of injured people has not yet been confirmed.
"The death toll has mounted to 20 even as the number of casualties is likely to go up further," Superintendent of Police (SP) S K Jha told PTI over phone.
Soon after the incident, locals gathered at the spot and attacked the driver of the train, leaving him seriously injured, railway sources said.
Jha said the engine of the Samastipur-Saharsa passenger train and an AC coach of Saharsa-Patna Rajyarani Express were set ablaze by angry locals gathered at the station under Samastipur division of East-Central Railway (ECR).
Chairman Railway Board Arunendra Kumar said the train was attacked and the driver was hurt.
He said it was a case of "trespassing" as the devotees were illegally trying to cross the tracks.
However, he refused to confirm any casualties. The agitation at the station has created obstacles in the way of carrying out rescue operations.
Unless the protesters vacate the site of the accident, it would be difficult for the railway and district authorities to carry out rescue work, railway officials said.
ECR Chief Public Relations Officer (CPRO) Amitabh Prabhakar said railway authorities spoke to the District Magistrate and the Superintendent of Police to provide police reinforcement so that medical aid could be rushed to injured persons before taking them to hospitals.