Updated 9.49am - Death toll rises

At least 90 people were killed and more than 150 injured when an Indian express train derailed in northern Uttar Pradesh today, with the toll set to rise amid a desperate scramble to locate survivors from the mangled wreck.

Police officials said about 20 people were still missing as authorities were trying to ascertain what caused 14 carriages of the train - travelling between the northeastern city of Patna and the central city of Indore - to suddenly roll off the tracks in Pukhrayan, 65 kilometres south of Kanpur city.

Amid scenes of desperation and anguish, survivors were looking for family members and some were also trying to enter the damaged carriages to rescue relatives and collect belongings, said senior railway official Pratap Rai.

"We are using every tactic to save lives but it's very difficult to cut the metal carriages," Rai said from the accident site.

The search for survivors is underway. Photo: Reuters

With the death toll set to rise further, the derailment could become India's worst rail tragedy since 2005, when a train was crushed by a rock and another plunged into a river - each killing more than 100 people.

India's creaking railway system is the world's fourth largest, ferrying more than 20 million people each day, but it has a poor safety record, with thousands of people dying in accidents every year, including in frequent train derailments.

Suresh Prabhu, India's Railways Minister, said in a tweet the government would immediately investigate the causes of the derailment and promised accountability with the "strictest possible action."

Authorities were checking if the air brakes that would have prevented the disaster failed, but added they would need to look further before concluding the reason behind the accidents.

Mangled carriages

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.

Rescue officials with yellow helmets were working their way through the crowds, carrying victims from the mangled wreckage as teams struggled to remove the derailed wagons from the tracks, one of the main transportation routes for goods and passengers in northern India.

The packed train, operated by the Indian government, derailed in the early hours of Sunday when more than 500 passengers were sleeping, survivors said.

"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.

Buses are being pressed into service to help passengers complete their journey, Singh said.

"I can see bodies lying near the tracks, everyone is in a state of shock. There is no water or food for us," said Rajdeep Tanwar, a survivor.

Push to modernise

Derailments and accidents have been a frequent occurrence, including an incident in Uttar Pradesh - India's most populous state - in March last year that killed 39 people.

Prime Minister Narendra Modi, who started out selling tea outside a train station, has promised to modernise India's railways and build high-speed engines befitting Asia's third-largest economy.

By some analyst estimates, the railways need 20 trillion rupees ($293.34 billion) of investment by 2020, and India is turning to partnerships with private companies and seeking loans from other countries to modernise its network.

Last year, Japan agreed to provide $12 billion of soft loans to build India's first bullet train.

On Sunday 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.