Beldanga SDPO Anandjit Hore confirmed that Aam Janata Unnayan Party chief Humayun Kabir was seized by Rejinagar police from his Murshidabad party office as polling proceeded.
Kabir, who had just voted, accused the police of hijacking booths and said 64 people had been detained in the last two months.
The Rejinagar bypoll, one of five contests across West Bengal, Tamil Nadu and Puducherry, opened on Tuesday, with the Election Commission scheduling a vote count for Oct. 9 and completion by Oct. 11.
The case will be heard by a court, and the police have assured that law and order are under control with CAPF support.