Thousands of people have queued up at polling stations in India's Bihar state for elections that are being seen as a test of PM Narendra Modi's popularity.
The BJP led by Mr Modi is battling a "grand" coalition of local parties, led by two former Bihar chief ministers - Nitish Kumar and Laloo Prasad Yadav.
More than 66 million voters are eligible to cast their ballots in 243 seats between Monday and 5 November.
Votes for the five-phase poll will be counted on 8 November.
Opinion polls are predicting a closely fought election.
Security is tight in nearly 13,000 polling stations in 49 constituencies on Monday. A total of 583 candidates are in the fray.
"Urging all those voting today in Bihar to vote in large numbers. I particularly urge my young friends to cast their vote," Mr Modi tweeted on Monday morning.
In the absence of a popular local leader, Mr Modi has led the campaign for his party and has addressed a number of well-attended campaign meetings.