Officials gave differing theories on what caused the derailment. Banerjee said it was caused by a bomb planted by suspected Maoist rebels. Surojit Kar Purkayastha, a state inspector-general of police, said rebels may have removed part of the track.
Rescuers at the scene used gas cutters to free passengers trapped in mangled coaches.
Medics brought at least 30 bodies to a nearby railway hospital in the town of Kharagpur, said E. Mitra, a doctor at the hospital.
The derailment took place in an isolated, rural stronghold of India's Maoist rebels, known as Naxalites, who have stepped up attacks in recent months and had called for a four-day general strike starting Friday.
Earlier this month, the rebels ambushed a bus in central India, killing 31 police officers and civilians.
The rebels, who have tapped into the rural poor's growing anger at being left out of the country's economic gains, are now present in 20 of the country's 28 states and have an estimated 10,000 to 20,000 fighters, according to the Home Ministry.
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