Results of these by-polls, which will be announced on June 5, will be keenly watched in the run-up to the 2014 general elections.
The highest voter turnout of 66 per cent was recorded in Howrah Lok Sabha constituency in West Bengal, followed by nearly 45 per cent polling in Maharajganj Lok Sabha seat in Bihar.
In Gujarat, the by-polls are being held for two Lok Sabha seats -- Porbandar and Banaskantha -- and four assembly seats. While Porbandar recorded 30 per cent polling, the turnout in Banaskantha was over 36 per cent.
The by-elections in Bharatiya Janata Party-ruled Gujarat are being viewed as a litmus test for opposition Congress, which had won all the six seats in last elections.
Banaskantha Lok Sabha seat fell vacant after the death of Congress Member of Parliament Mukesh Gadhvi.
In Porbandar, the elections are being held to fill the vacancy caused by the resignation of Vitthal Radadiya, who hit the headlines for pulling a gun at a toll booth attendant.
Radadiya had quit Congress in February and crossed over to the BJP, which has fielded him for the Lok Sabha by-polls.
In West Bengal, voting was held for the Howrah Lok Sabha seat, where the by-election was necessitated by the death of Trinamool Congress MP Ambika Banerjee.
The election assumes significance as it comes just ahead of panchayat elections in the state.
The seat is witnessing a triangular contest among TMC, Congress and Communist Party of India - Marxist in a field of 13 candidates.
The ruling Trinamool Congress has fielded former India football captain Prasun Banerjee, while Congress has fielded lawyer Sanatan Mukherjee and CPI-M has fielded Sridip Bhattacherjee, a former party district secretary.
BJP is not contesting in Howrah on the instructions of its national president Rajnath Singh. It is seen as a move to keep the door ajar for TMC, a former National Democratic Alliance ally. However, local BJP leader Ranjan Pal is in the fray as an Independent.
Congress and TMC, which have parted ways, had fought the seat jointly in 2009.
CPI-M is hoping to cash in on the division of votes between TMC and Congress this time.
For Congress, the by-election is important as a defeat could mean a setback for the party before the panchayat polls as well as next year's Lok Sabha election.
Congress has already lodged a complaint with the Election Commission, alleging that Trinamool Congress workers threatened voters in the presence of micro-observers at some booths in Howrah.
The Election Commission for the first time used the GIS-SMS based poll monitoring system, android-based counting application and live monitoring of sensitive areas.
In Bihar, a keen contest was witnessed in Maharajganj Lok Sabha seat, where ruling Janata Dal - United nominee Prashant Kumar Sahi, who is also state education minister, Rashtriya Janata Dal’s Prabhunath Singh and Jitendra Swami of Congress are crossing swords to fill the vacancy caused by the death of RJD MP Uma Shankar Singh.
By-polls were also held for four assembly seats in Gujarat -- Dhoraji, Jetpur, Limbadi and Morva Hadaf. The average turnout was 38 per cent in these seats.
In Uttar Pradesh, polling was held to fill the Handia assembly seat following the death of sitting Samajwadi Party MLA Mahesh Narayan Singh.
The SP, which is in power in the state, has fielded Singh's son Prashant, apparently to cash in on the sympathy factor.
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