Houses of two local Trinamool Congress leaders, who run the sand mine business, were also ransacked by a mob.
A dumper carrying sand rammed into the cycle of the farmer injuring him seriously. He was first taken to a local hospital from where he was referred to a hospital in Kolkata.
Following the accident, local villagers attacked its office near Bhagirathi river and set fire to it, police said.
They alleged that bombs were stockpiled in the office which also exploded severely damaging the office.
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At least three vehicles used in the mining business were also torched.
The mob also ransacked the houses of local Trinamool Congress leaders Ashish Shikdar and Kalyan Biswas.
While Shikdar or Biswas could not be contacted, Shanku Chakraborty, another person involved in the business, said the dumper that hit the farmer did not belong to them.
Denying that bombs had been kept in the office, he said barrels of diesel were there which exploded.
None was arrested.