Voting for the high-voltage bypoll to the Bhabanipur seat in south Kolkata, where West Bengal Chief Minister Mamata Banerjee is contesting, has begun. The all-important Bhabanipur bypoll would see BJP's Priyanka Tibrewal and CPI(M)'s Srijib Biswas locking horns with Trinamool Congress (TMC) chief Mamata Banerjee, who needs to win the election to retain her seat as state CM.