Eleven persons were injured when two rival groups fought and hurled low-intensity bombs at each other during the elections at Banonagar High School at Ousgram near Guskara in Burdwan district.
Five policemen, including the SDPO Kazi Mohammed Hussain, were also among the injured.
Six persons have been detained in this connection, sources said, adding that more senior police officers have been rushed to the spot with reinforcements.
In a separate incident in East Midnapore district's Moyna block, 12 persons were injured when rival factions fought during similar election of Sukantu Vidyapith in Chandrachowk village, police said.
Police rushed to the spot and brought the situation under control. Rapid Action Force (RAF) have been deployed in the area, they said, adding two persons have been detained in this connection.