The three districts where election would be held are Murshidabad having 22 seats, Birbhum-11 and Nadia-17. In all 11,531 polling stations have been set up.
Tight security arrangements have been made in all three districts to ensure free, fair and peaceful election.
Police sources said about 4800 security personnel including central para-military personnel have been deployed in the three districts.
Defying the party's warning, four rebel Congress candidates backed by party MP Adhir Chowdhury are contesting as independents in Murshidabad district and an equal number of dissidents are in the fray in Nadia. All of them have been suspended by the party.
Congress president Sonia Gandhi and union Finance minister Pranab Mukherjee, an MP from Murshidabad and Trinamool Congress chief Mamata Banerjee campaigned in the districts urging voters not to vote for any rebel candidate and utilise the opportunity to oust the Left Front government.
Prominent Left leaders who campaigned included Chief minister Buddhadeb Bhattacharjee in Nadia besides CPIM politburo member Biman Bose and Housing minister Gautam Deb.
BJP veteran L K Advani and party chief Nitin Gadkari also took part in the campaigning.
The main poll plank of Trinamool Congress-Congress combine is for ushering in ''paribartan'' (political change) in the state ruled by CPIM-led Left Front for the last 34 years.
Chief minister Buddhadeb Bhattacharjee has ridiculed the slogan for change.
Prominent candidates whose fate would be decided are Union Finance minister Pranab Mukherjee's son Abhijit Mukherjee from Nalhati, Panchayat minister and CPI(M) leader Anisur Rehman, former High Court judge Nure Alam Chowdhury contesting on Trinamool Congress ticket from Murarai and Rukbanur Rehman, brother of computer graphics teacher Rizwanur Rehman from the Chapra constituency.
CPIM has fielded candidates in 31 seats followed by TC in 29 and Congress in 21 seats. BJP has put up nominees in all the 50 constituencies and Bahujan Samaj Party in 27 seats.