Indians began voting in a month-long general election on Thursday with a violence that killed Indian soldiers and Maoist insurgents.
A total of 124 seats in the Lok Sabha, or lower house of parliament, are up for grabs in Thursday's polls.
Neither of the two main national parties - the incumbent Congress party and the Bharatiya Janata Party (BJP) - is seen as capable of securing an absolute majority.
About 714 million people are eligible to cast ballots. The results are expected on May 16. Exit polls are banned.
Maoists killed five election officials in a landmine blast in Chhattisgarh state. Ten police were killed in other attacks across India's central and eastern "red belt" where Thursday's election was centred.
The government has deployed hundreds of thousands of police to protect more than 140 million people who can vote on Thursday in polls.
Prime Minister Manmohan Singh has described Maoist violence as India's biggest internal security threat.
Vote on religious and ethnic ties
Some election officials rode elephants to remote polling stations near the Myanmar border. Other ballots were brought by two-day sea trips to the Andaman Islands in the Bay of Bengal.
In Varanasi, the northern sacred city on the Ganges River known for its Hindu gurus, many voters arrived on bicycles and bullock carts to cast electronic votes.
Women in saris or burqas, often carrying children, pressed buttons with pictorial symbols of each party, after their fingers were marked with ink to avoid fraud.
"Nowadays there are so many small parties, previously there used to be only one or two big parties," said Mohammed Mustaquim, waiting to vote in Varanasi. "This makes choosing difficult."
Ancient caste, religious and ethnic ties will play a huge role in the vote as well as national problems like the slowdown, security fears and local issues from the building of a village water pump to problems of wild elephants trampling on villagers.
Current Prime Minister Manmohan Singh, 76, is squaring off against L.K. Advani of the Hindu nationalist Bharatiya Janata Party (BJP).
Advani has publicly accused Singh of being a weak prime minister, saying that "he has devalued this post".
The normally mild-mannered Singh has also criticised Advani, recalling his role in the controversial demolition of a mosque in 1992 and the anti-Muslim riots that occurred when the party was last in power.
Singh, an Oxford-educated economist, was picked by Gandhi to be prime minister after the 2004 elections.