Twelve coaches of the Assam-bound Bikaner-Guwahati Express train derailed near Domohani in the state's Jalpaiguri district on Thursday, according to the authorities.
Among the injured, six are in critical condition and have been shifted to North Bengal Medical College and Hospital in Siliguri, broadcaster NDTV reports. The others are being treated at hospitals in Jalpaiguri and Maynaguri.
All the survivors were evacuated by midnight and no more passengers are trapped in the derailed coaches, officials said at the end of a rescue mission.
Earlier, Jalpaiguri District Magistrate Moumita Godara Basu said four bodies were found at the accident site and three others died at the hospital, according to Hindustan Times.
"Since some of the injured are in a critical condition, the toll may go up. We are now using cranes for removing the damaged compartments," she said on Thursday, adding rescuers thoroughly searched each coach for survivors and bodies through darkness and thick fog.
The train had 1,053 passengers on board at the time of the derailment, the Northeast Frontier Railway said.
It was running nearly three hours late during its three-day journey, havinf started from Bikaner late on Wednesday night. The train was supposed to reach Guwahati early on Friday morning.