Fourteen carriages of the Patna-Indore Express train were thrown off the tracks in the early hours of Sunday near the Kanpur Dehat district, officials said.
Bodies of 91 people have been so far recovered from the damaged carriages, 'The Hindu' reported quoting Kanpur's Superintendent of Police Pravakar Choudhury.
"The incident, which took place at around 3am, also left over 150 others injured," Kanpur range police chief Zaki Ahmed told IANS.
More than 30 ambulances had been pressed into service, Ahmed said, adding that over 250 police officials were helping carry out rescue and relief operations.
Reuters quoted a senior railway official in New Delhi Anil Saxena saying "Still many more passengers are trapped."
Railways Minister Suresh Prabhu said that a probe has been ordered.
"All rescue relief work on to deal with unfortunate accident. All medical and other help rushed. Enquiry ordered. Situation monitored closely," he tweeted.
In March last year, 39 people were killed and 150 were injured in a train disaster in Uttar Pradesh.
Prime Minister Narendra Modi took to Twitter to express his condolences.
"Anguished beyond words on the loss of lives due to the derailing of the Patna-Indore express. My thoughts are with the bereaved families," Modi said.