"While nine persons died at the spot one person died at a hospital. Ten others who are injured have been admitted to nearby hospitals," said local Trinamool Congress lawmaker Samir Panja. Police had initially put the toll at six.
The people in Pancharul village were returning home after an idol immersion ceremony and had taken refuge in a temple in the rain when they were struck by the bolt.
Chief minister Mamata Banerjee has announced a compensation of Rs.2 lakh each to the families of the deceased.
The condition of some of the injured was said to be serious.