Voting has begun in crucial elections in India's northern Bihar state, which is being widely seen as a test of Indian 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.
Polling is being held in 49 constituencies in 10 districts 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.
'Grand alliance'
Correspondents say the prime minister is taking no chances in the state, and plans to hold some 20 public meetings in the next few weeks.
"A BJP government in Bihar will help us work seamlessly to create jobs for the youth, look after our farmers and ensure overall development, which is the antidote to every single problem," Mr Modi told a packed meeting last week.
A BJP win will further demoralise India's opposition parties - who are yet to recover from last's year debacle in the general election - and will reinforce the belief that the Hindu nationalist party remains invincible despite February's drubbing in state polls in Delhi, says the BBC's Soutik Biswas.
Also, a substantial win will help BJP get more seats in the upper house of parliament in Delhi, where it lacks a majority, making it easier for the government to pass key legislation for economic reforms.
A win by the "grand alliance" - Janata Dal (United) and Rashtriya Janata Dal - will give the opposition a major shot in the arm.
Regional parties will be enthused to forge similar alliances to contest upcoming major elections in states like Uttar Pradesh - which promises the mother of all battles - in 2017, our correspondent says.
Although Mr Modi has campaigned on the promise of jobs and growth, a growing controversy over the issue of banning cow slaughter threatens to polarise voters on religious lines.
India's Hindus consider cows sacred and since Mr Modi took over as prime minister, several BJP-ruled states have tightened laws protecting cows.
Emotions over the issue have been running high following the lynching of a 50-year-old man in the northern state of Uttar Pradesh, allegedly over rumours that his family had been storing and consuming beef at home.
Bihar elections
Total voters: 66.8 million
Constituencies: 243
Number of polling stations: 62,779
Voting will be held in five phases from 12 October to 5 November
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