An Election Commission official told IANS: "Voter turnout of 42 percent was recorded till 1 p.m."
The by-polls are being held at Nalhati in Birbhum district, Rejinagar in Murshidabad district and English Bazar in Malda district.
The by-elections were necessitated after sitting Congress legislators from Rejinagar and English Bazar left the party and joined the Trinamool Congress.
The assembly seat at Nalhati fell vacant after Congress legislator Abhijit Mukherjee won the election at Jangipur parliamentary seat, vacated by his father Pranab Mukherjee, who was elected president of India.
The English Bazar seat has six contestants, and a 208,204-strong electorate.
The elections could prove a litmus test for both Chief Minister Mamata Banerjee-led Trinamool Congress and the Congress. The alliance of the two parties ended last September.
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