The accident took place near Rura in Kanpur, the official added.
The number of injured has risen to 43 since early morning, Inspector General of Police (Kanpur range) Zaki Ahmed said.
He also said that at least 10 passengers were shifted to a Kanpur hospital for better treatment.
The coaches of the Ajmer-bound train derailed near Rura, about 50 km from Kanpur around 5.20 a.m.
Of the derailed coaches, 13 were sleeper class, while two were general coaches, the official said.
Senior railway, district and police officials have rushed to the accident site for rescue and relief operations. Those critically injured were rushed to Akbarpur earlier, the district headquarter of Kanpur (rural).
The others injured were rushed to a Community Health Centre in Rura.
A medical train has been sent from Lucknow to the accident site, a Northern Railway (NR) official said and informed that helpline numbers were also issued in Kanpur, Lucknow and Allahabad.
Two of the coaches fell in a ‘nehar’ (canal), leading to fears of more injuries and even casualties.
Following the accident, routes of at least 21 trains were diverted, North Central railway official Amit Malviya said.
Railway Minister Suresh Prabhu has ordered a thorough probe into the accident.
This was for the second time in the last 38 days that a train accident has occurred in Kanpur. The earlier one happened on November 20, leaving more than 150 dead.
Railway Minister Suresh Prabhu on Wednesday ordered a thorough probe after the Sealdah-Ajmer Express derailed in Uttar Pradesh early morning.
“Personally monitoring the situation in the wake of unfortunate derailment of Sealdah-Ajmer Express near Kanpur,” Prabhu said in a series of tweets.
“Thorough investigation will be carried out to ascertain the cause,” he added.
The Railway Minister also said that he has directed senior officials to reach the accident site immediately.
“Immediate medical help being provided to the injured. Mobilised resources, directed all concerned to ensure rescue and relief,” he said.
At least 40 passengers were injured as 15 coaches of the train derailed near Rura, 50 km from Kanpur.
“Ex gratia will be paid to injured. All passengers are being provided with necessary assistance to ensure least inconvenience. Doing our best,” the Railways Minister said.
“Directed Chairman Railway Board, all senior officials to personally ensure best possible help. Medical vans, relief vans were rushed immediately. Officers are on spot,” Prabhu said.
The Railways Minister further said that the “injured have already started getting medical care, doctors are attending to all. We are working with hospitals and district administration to offer all possible help”.