According to the Election Commission sources about 74.89 per cent votes were recorded till 3pm.
With the polling continuing till 5 pm the final vote percentage is awaited.
The EC said the election was by and large peaceful and it is looking into complaints by the opposition parties.
Polling in the constituency is being held amid tight security with eight companies of central forces deployed, he said.
The opposition CPI(M) and BJP have accused the ruling TMC of driving away their election agents from the polling booths, which was denied by TMC leader and Rajya Sabha lawmaker Manas Bhunia.
State BJP president Dilip Ghosh criticized TMC for resorting to terror during the polls.
"The election results will not reflect the real mandate of the people. The people of Sabang could not vote freely and fairly due to the terror tactics of TMC," he said.
Mr Ghosh's view was echoed by CPI(M) and Congress.
"The TMC has been doing this in each and every election. They know that they will lose Sabang and that is why they resorted to violence," Leader of opposition and state Congress leader Abdul Mannan said.
The TMC, however, denied the allegations and said the people have voted in favour of Chief Minister Mamata Banerjee's developmental politics.
"The allegation made by the opposition parties is completely baseless. Voting is peaceful in the constituency," Bhunia said.
TMC has fielded Ms Gita Rani Bhunia, wife of Mr Manas Bhunia, a former Congress MLA who had defected to the Mamata Banerjee-led party earlier this year necessitating the by election.
Mr Bhunia had won the seat in last year's assembly polls.