Trouble began after 15-20 anti-socials barged into the Zilla Parishad conference hall where representatives of cooperative societies had started assembling for voting.
A police officer said the anti-socials pelted stones, hurled bombs and the police used rubber pellets to disperse them.
Seven persons, including the IC of Raiganj police station and a police constable, were injured in the incidents.
Five of the injured were admitted to a Raiganj hospital from where two persons have been referred to North Bengal Medical College and Hospital in New Jalpaiguri.
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He, however, did not divulge the identity or political affiliation of the anti-socials.
Fifteen CCTV cameras were also damaged by the anti-socials.
The CPI(M) alleged that a few of the TMC staff tried to prvent the voters from casting their votes, which prompted the violence.