Tens of millions of Indians have voted in phase one of the country's first all-electronic election.
Hundreds of millions are expected to take part over three weeks
Every vote in the world's largest democracy is being recorded at the press of a button.
Authorities said polling had been fairly peaceful despite violence in Jammu and Kashmir and the north-east.
Over 670 million people can vote in four main phases staggered over three weeks, partly to allow the deployment of two million security officers.
A quarter of the electorate were eligible to take part in Tuesday's voting, which was spread across 13 states and three union territories.
"By and large, things were under control. So far it has been a relatively peaceful poll," Deputy Election Commissioner AN Jha said.
He said turnout was 50-55%, compared to just under 60% overall in 1999.
Observers blamed hot weather and a lacklustre campaign.
Television exit polls, which have a mixed track record in India, gave the ruling Hindu
nationalist-led coalition a lead in early voting over the main opposition Congress party.
BBC News Online's Soutik Biswas in Delhi says, despite the isolated outbreaks of violence, day one of the election was by and large peaceful.
At least 15 people were reported to have been killed by the end of polling. That contrasts with some 100 deaths throughout the whole of the 1999 elections.
Correspondents described the logistics of providing electronic voting machines at all 700,000 polling stations as mind-boggling - helicopters, bullock carts and elephants were all used to ferry the machines to the remotest corners of India.
Despite early reports of a few minor glitches, the voting machines seem to have worked well on the whole.
Much media attention has been paid to the struggle between the two main parties - the Hindu nationalist Bharatiya Janata Party, which leads the ruling coalition, and Congress, the main opposition party.
But BBC South Asia correspondent Adam Mynott said that for many - if not most voters - it would be local matters that weighed on their minds when they entered the polling stations.
In Indian-administered Kashmir, there was violence minutes after polls opened at 0700 local time (0130 GMT).
"I think it is not right that many young people are indifferent about voting."
Shailaja Ramana, Hyderabad
At least one soldier was reported killed and six civilians injured when suspected militants attacked two polling stations in the disputed state.
The militants have been threatening to disrupt the elections and the turnout was low in most areas being polled.
However, in some areas people expressed their delight at being able to vote in peace for the first time in a decade, thanks to the current ceasefire in the region between India and Pakistan.
Mohammad Afzal, the first voter at the polling station in the Kashmiri village of Chainabal, was not put off by the threats from separatist militants.
"I came to vote because wasting one's ballot in a democracy is a sin," he told the BBC.
There was also violence in the north-eastern states of Manipur and Jharkhand where Maoists have called for a boycott.
Despite the violence, polling was said to be brisk across most of the north-east.
Meanwhile, in Bangalore in the south early voters were frustrated by teething problems with voting machines.
"I came in to vote at 0630 and it's an hour now. How long can I wait? I want to vote and go back home," one woman said.
Analysts say Tuesday's vote was being seen as a test.
"The first round is administratively very important," Ashutosh Varshney of the University of Michigan told BBC News Online.
Voting 20, 26 April and 5, 10 May
Counting of votes on 13 May
675 million eligible to vote
543 MPs elected for five years
1 million voting machines
Log up to five votes a minute
"If they are conducted peacefully, that will set a trend. And if violent, the first round will make a doubling of administrative effort necessary to keep peace."
Prime Minister Atal Behari Vajpayee called the election five months early, hoping to cash in on a "feel-good factor".
Mr Vajpayee can point to an economy set for 8% growth this year and recent peace moves with Pakistan as his administration's key achievements.
These have helped give the ruling BJP-led alliance a lead in many opinion polls, although these have often proved unreliable and the fight may be closer than earlier expected.
Congress, led by Sonia Gandhi, says the growth has not benefited the rural poor and is unimpressed by the peace process with Pakistan.
The party also plays on the BJP's Hindu nationalism, saying it threatens the country's secular tradition.
The last day of voting is 10 May, with results due on 13 May.