Indians have begun voting in the world's biggest election, which is set to sweep the Hindu nationalist opposition to power at a time of low growth, anger about corruption and warnings about religious unrest.
India's 814-million-strong electorate are forecast to inflict a heavy defeat on the ruling Congress party, in power for 10 years, and elect hardliner Narendra Modi from the Bharatiya Janata Party (BJP).
Voting began at 7.00am (1230 AEDT) on Monday in six constituencies in tea-growing and insurgency-racked areas of the northeast, an often neglected part of the country wedged between Bangladesh, China and Myanmar.
The marathon contest, to be held over nine phases until May 12, got under way after a bad-tempered campaign which reached new levels of bitterness at the weekend.
Amit Shah, one of Modi's closest aides, faces a judicial investigation after he reportedly told supporters to see the election as "revenge" against a "government that protects and gives compensation to those who killed Hindus".
Rahul Gandhi, leading Congress into his first national election as scion of the famous dynasty, warned Sunday that a victory for Modi threatens India's religious fabric.
"Wherever these people go they create fights. They'll pit Hindus and Muslims against each other," he warned on Sunday.
Prime ministerial front-runner Modi, the hawkish son of a tea seller whose rise has split his party, is a polarising figure due to his links to anti-Muslim religious riots in 2002.
Releasing the party's delayed manifesto on Monday, which mixed promises for economic development and the protection of Hindu interests, Modi promised to lift the mood of the country.
"Today the country has become stagnant. It is drowned in pessimism. It needs momentum to move forward," he said.
Over the last a decade, growth has averaged 7.6 per cent per year, yet inflation has also been high and a sharp economic slowdown since 2012 has crippled the public finances and led investment to crash.
Coupled with a widespread perception that Prime Minister Manmohan Singh's second term since 2009 was largely lost to indecision and scandal, Modi has been able to tap into a groundswell of discontent.
The election will be the biggest in history and is a mind-boggling feat of organisation as voters travel to nearly a million polling stations.
Such is India's population growth that 100 million people have joined the electoral rolls since the last vote five years ago. More than half of the country is aged under 25.
Modi, 20 years older than Gandhi at 63, is expected to score strongly among the young thanks to his message of aspiration and skills over the left-leaning Congress's pitch of welfare and equitable development.
But many observers worry about his domestic impact in an officially secular country.
In 2002, more than 1000 people, mostly Muslims, died in violence shortly after Modi became chief minister, leading the United States and European powers to sanction him for more than a decade.
