Thirteen coaches of the Kalka Mail passenger train left the rails near the town of Fatehpur in Uttar Pradesh.
Rescue workers and locals arrived to try to free trapped passengers from the badly damaged carriages.
The train was travelling from Howrah near Calcutta to the capital Delhi. There are fears that the death toll could rise.
'Upside down'
The BBC's Sanjoy Majumder in Delhi says Prime Minister Manmohan Singh has expressed his deep concern over the accident, the second in a week in Uttar Pradesh, and has directed the railway authorities to use all available resources for the relief operation.
Soldiers have been deployed to help in the rescue effort.
The cause of the derailment, about 120km (75 miles) south-east of Uttar Pradesh's capital, Lucknow, was not immediately clear.
Television footage showed carriages at skewed angles, with one on the roof of another and a third thrown clear of the train.
One passenger told CNN-IBN television: "We were sitting in our seats when suddenly everything turned upside down. When the train stopped we broke the glass windows to jump out on the track."
State police official Brij Lal told the Associated Press news agency: "We're trying to cut into the coaches and rescue those still trapped."
The driver was among those injured.
The number of people on board was not immediately clear but reports said there may have been up to 1,000 passengers.
Accidents are common on the state-owned Indian railway, an immense network connecting every corner of the vast country.
It operates 9,000 passenger trains and carries some 18 million passengers every day.
On Thursday, 38 people died in Uttar Pradesh when a train hit a bus carrying a wedding party.
