Neither of the two main national parties -- the incumbent Congress and the Hindu nationalist Bharatiya Janata Party (BJP) -- is seen as capable of securing an absolute majority in the five-stage polls.
With a slew of regional and local parties expected to grab up to 50 percent of the 543 parliamentary seats on offer, the final result will kick off an intense period of political horse-trading as the big players rush to form a viable coalition.
The prospect of a patchwork government with no united policy is a bleak one, with India facing a sharp economic downturn and increasing domestic and regional security concerns.
"What we need is a government which will pull India through these difficult times," said political analyst Rasheed Kidwai.
"The tragedy is that the influence of the main national parties has shrunk so much. The regional parties which are on the rise, are without the national outlook needed at this stage," Kidwai said.
More than 700 million Indians are eligible to vote in the world´s largest democratic exercise, with around 143 million registered for the first phase alone.
Thursday´s ballot will take in large swathes of northern and eastern India, including areas beset by a range of violent insurgencies involving tribal rebels, Maoist guerrillas and Muslim militants.
In order to ensure voter safety, more than two million security personnel will be rotated around the country over the five phases of balloting that end on May 13. Final results are to be announced on May 16.
The leading candidates for prime minister are both veterans. The incumbent, Manmohan Singh of the Congress Party, is 76, while his main challenger, the BJP´s L.K. Advani, is even older at 81.
The only viable alternative to a Congress- or BJP-led coalition is provided by a loose alliance of left-leaning and regional parties called the "Third Front."
Negotiations are ongoing, but the alliance may join forces with Mayawati Kumari -- the self-styled champion of the lower castes who has made no secret of her ambition to become India´s first "untouchable" prime minister.
Yashwant Deshmukh, who heads a public polling agency, warned that a shaky coalition would be unable to implement tough economic reforms for fear of losing support.
"If you have an unstable government, chances are that the decisions it takes will be populist and protectionist in nature, and that will impact adversely on market reforms," Deshmukh said.
"Still, whatever government emerges is not going to last more than two years," he added.
Many voters are expected to make their choices along religious and caste lines or on the basis of strictly regional issues that impact their daily lives.
Any new government´s room to fix problems will be sharply curbed by lavish spending in the past on a national jobs scheme, farm loan waivers, civil service wages hikes, tax cuts to spur growth and other steps.
India´s fiscal deficit for the last financial year was six percent of GDP -- more than double the target -- and 11 percent if the states´ deficits are included.
The campaign has become heated at times, causing the Election Commission to condemn unnamed party leaders for speeches "inciting communal hatred."
One high-profile candidate, Varun Gandhi -- a black sheep of the Nehru-Gandhi political dynasty -- was jailed after threatening to cut off the hands of anyone who dared harm India´s majority Hindus.
Rival party leaders traded last-minute barbs on Wednesday, with Advani labeling Singh "a puppet" of Congress president Sonia Gandhi, to which Gandhi responded that Advani was "a slave" to right-wing Hindu organizations.
The regions voting on Thursday include sensitive areas of Kashmir near the Pakistan border and northeastern states on the frontier with Bangladesh.
"We have heightened our vigilance along the borders. Infiltration attempts are a serious matter," said the head of the paramilitary Border Security Force, M.L. Kumawat.
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