The goods train derailed in Gaya-Mughalsarai section of the East Central Railway on Thursday night.
"Prime facie, it seems there was a technical fault in the rail line. But the real cause of the derailment would be ascertained after an inquiry," Amitabh Prabhakar, spokesperson of East Central Railway, said.
The goods train was coming from Dhanbad to Mughalsarai junction.
The derailment has caused damage to tracks and disrupted regular train services in the grand cord.
"We are diverting all passenger trains to different routes as all the three lines between Gaya and Mughalsarai are blocked due to the derailment," said Prabhakar, adding, "The main focus now is on restoring the line."
Asked how soon the train service on the line will be restored, he said it will take about 48 hours to restore the line completely.
"The movement of goods train has been suspended on the affected route and the priority is to divert the passenger trains," he said.
Ninety trains including the Howrah Rajdhani, Bhubaneswar Rajdhani, Sealdah Rajdhani and Jammu Tawi Mail are being diverted to the Gaya-Patna route. Sealdah-New Delhi Duronto Express has been diverted towards Gomo-Barka-Chunar route while the Howrah-Kalka Mail has been diverted to the Jhaja-Patna-Mughalsarai route.
Senior railway officials have reached the site to supervise the rescue and restoration operation. A relief train has been sent to the accident spot from Mughalsarai.
Northern Railway has opened several helpline numbers to assist passengers.
Helpline numbers are operational at Old Delhi station (011-23962389, 011-23962332), New Delhi (011-23341074, 011-23342954), Varanasi (0542-2504658) and Lucknow (0522-2635844, 09794830973, 09794830975).
Northern Railway officials said adequate arrangements have also been made to provide tea, water and refreshments to the passengers of trains regulated at Varanasi, Kashi and Vyas Nagar stations of Lucknow division.
Facilitation centres have also been opened at major railway stations which are being manned by railway officials.