India's authorities have mounted a huge security operation in the tiny north-eastern state of Tripura around Thursday's general election vote there.
Voter turnout on Tuesday was reported lower than in 1999
Thousands of police and troops are being deployed to counter the threat from separatists who oppose the polls.
A quarter of India's 670m electorate had the chance to vote in the first round on Tuesday.
Parties are now readying for the second main phase, which includes key northern states like Uttar Pradesh and Bihar.
Polls opened on time in Tripura and small queues were reported of voters waiting to cast their ballots.
The state has just two of India's 543 parliamentary seats - both of which were won last time by communists.
The state was originally due to vote on 20 April but polling was put back by two days because of a local festival.
Separatists have vowed to disrupt the election - and the authorities say they are not taking any chances.
Election teams have been airlifted to remote polling stations because of the rebel threat.
State police chief GM Srivastav said paramilitary soldiers had wounded and captured a number of rebels in shoot-outs since the weekend.
"The threat from insurgents to the election remains," he told Reuters news agency.
Security along the border with Bangladesh has been beefed up to stem incursions from rebels who, India says, are based in camps in Bangladesh.
Dhaka denies the charge.
Meanwhile, leaders of the ruling Bharatiya Janata Party and the opposition Congress headed to Uttar Pradesh on Wednesday ahead of Monday's key vote.
The state has a population of some 170m. Along with neighbouring Bihar it returns over a quarter of India's MPs.
"I think it is not right that many young people are indifferent about voting."
Shailaja Ramana, Hyderabad
Prime Minister Atal Behari Vajpayee and Congress leader Sonia Gandhi are both contesting constituencies in Uttar Pradesh.
Exit polls, which have a mixed track record in India, show the BJP in the lead after round one, but with Congress narrowing the gap.
"The first phase of voting has been encouraging for us, it will help us to do well in the subsequent states," BJP spokesman Mukhtar Abbas Naqvi told Reuters.
Congress says it is confident it has done well.
"I am opposed to these exit polls, I don't believe in their veracity," party spokesman Kapil Sibal said.
Voter turnout in the first phase was 50-55%, compared to just under 60% overall in 1999.
Polling was marred by sporadic violence in Jammu and Kashmir, and the north-eastern states of Jharkhand and Manipur.
At least 15 people were reported to have been killed across the country by the end of the day. About 100 lost their lives during the whole 1999 campaign.
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
Revotes will take place at 213 polling stations which faced disruption on day one, the Election Commission announced on Wednesday.
The last day of voting is 10 May, with results due on 13 May.
Mr Vajpayee and his BJP hope to cash in on a "feel-good factor" brought about by a strong economy and peace moves with Pakistan.
Congress argues the rural poor have been left out and says attacks on its leader's Italian roots are unfair.
The party also says the BJP's Hindu nationalism threatens the country's secular tradition.