Rescue teams worked through the night with cranes and cutters to disentangle the train before police halted the search for missing people.
The death toll from a train which derailed in India increased to 142 on Monday.
Over 200 people were injured when several carriages of an express train derailed in northern India early Sunday morning.
Indian rescuers on Monday called off a search of the mangled carriages after pulling more bodies from the wreckage.
The derailment was India's deadliest train tragedy since 2010 and has renewed concern about poor safety on the state-run network, a lifeline for millions that has suffered from chronic under-investment.
Rescue teams worked through the night with cranes and cutters to disentangle the train before police halted the search of the 14 carriages that derailed in the early hours, while most passengers slept.
Police are trying to determine what caused carriages of the train travelling between Patna and Indore to suddenly roll off the tracks in Pukhrayan, 65 kilometres south of Kanpur city.
Authorities say they are checking the condition of the tracks, but would need to look further before concluding the cause of the derailment, India's deadliest rail tragedy since more than 140 died in a 2010 collision in West Bengal.
The accident took place early in the morning when most of the passengers were still asleep.
"Suddenly I could feel that the carriage was overturning. I immediately held the metal rod near the bathroom door," said Faizal Khan who was travelling with his wife and two children, all of whom survived the accident.
Kanpur is a major railway junction and hundreds of trains pass through it every day. Several trains using the line have been diverted to other routes, Anil Saxena, spokesman for Indian Railways, said in New Delhi.
TV footage showed badly mangled blue carriages, with crowds of people and police on top of the wreckage searching for survivors. One carriage was almost lying on its side, and appeared to have been completely torn apart.
There were more than 500 passengers on the train, and senior railway official Anil Saxena said "many were still trapped"
Rescuers used gas cutters to open the derailed coaches to reach those trapped inside, while cranes were deployed to lift the coaches from the tracks.
Medical teams were providing first aid near the site while the more seriously injured were moved to hospitals in Kanpur.
India's railway network, one of the world's largest, is still the main form of long-distance travel in the vast country, but it is poorly funded and deadly accidents occur relatively frequently.
In 2014, an express train ploughed into a stationary freight train, also in Uttar Pradesh, killing 26 people.
And last year 27 people died after two trains derailed in central Madhya Pradesh state during heavy rains.
India's Prime Minister Narendra Modi tweeted that he was "anguished beyond words" by the loss of life in the latest accident.