Around 8 lakh voters on Thursday exercised their franchise in the first two hours of polling in the by-election of Bihar's Bankipur assembly seat, an official said.
The voting began at 7 am in 422 polling stations and will continue till 6 pm.
"The polling has so far been peaceful. The voter turnout till 9 am was 4.61 per cent," the official said.
Altogether 26 candidates, including Jan Suraaj Party founder Prashant Kishor, are in the fray.
Kishor, 49, a former poll strategist who launched the Jan Suraaj Party a few years ago, is contesting his first election, while the BJP, which has never lost the seat since 1995 when it was known as Patna West, has fielded low-key youth wing leader Neeraj Kumar Sinha.
Kishor's entry has intensified the contest in a constituency where the BJP has won by huge margins over the years.
Nabin, who gave up the seat in April upon election to the Rajya Sabha, had won the assembly segment for the fifth consecutive time in November last year, defeating nearest rival Rekha Gupta, the RJD candidate fielded by her party again this time, by over 50,000 votes.
Prominent politicians among those who voted till 9 am include senior BJP leader CP Thakur, his son and Nawada MP Vivek Thakur and state minister Ramkripal Yadav.
Nabin appealed to electors to come out in large numbers and cast their votes to strengthen the resolve of a developed India.
"I appeal to all the voters of the Bankipur (Bihar), Manjalpur (Gujarat) and Datia (Madhya Pradesh) assembly constituencies, especially the youth and women, to come out in large numbers to cast their votes and make their invaluable contribution toward strengthening the resolve of a Vikashit Bharat," he wrote in his X post.
BJP's Bihar unit president Sanjay Saraogi also urged people to exercise their franchise early in the day for the development of Bankipur.
(With inputs from PTI)