Railways said it would take another 24 hours to completely restore the service.
The derailment of the goods train near Mughalsarai last night has almost shut down the busy route, leading to diversion and cancellation and late running of scores of trains, causing inconvenience to passengers.
"We would be able to restore only one track by tonight and hope to open both the up and down lines by tomorrow night...We have taken up the restoration work on a war-footing," East Central Railway spokesperson Amitabh Prabhakar said in Delhi.
So far 13 of the 26 coal-loaded wagons which derailed have been removed from the tracks. Senior Railway officials were camping at the site and overseeing the track restoration work.
Prabhakar said Railways have already ordered an inquiry into the derailment which would be conducted by a senior official.
The Delhi-Howrah grand chord line is considered as one of the vital links in Indian rail network as it not only connects the capital with eastern part of the country, but also covers the coal belts and steel plants in Jharkhand, Odisha and Bengal.
Rajdhanis to Howrah, Sealdah and Bhubaneswar have been rescheduled from New Delhi tonight as several long-distance trains from the east continue to arrive in the capital several hours behind schedule.