More than two million officers have been deployed to prevent unrest during the election, which will use more than 1.3 million electronic voting machines in 828,804 polling stations.
However, there were scattered reports of violence by suspected Maoist fighters in several states on Thursday.
S Y Quraishi, India's chief election commissioner, told Al Jazeera that polling was disrupted by violence at about 60 or 70 polling stations.
"If you look at the magnitude of the exercise that is not such a shocking number ... considering we had 180,000 polling station operating today," he said.
Five election officials were killed in an explosion in Chhattisgarh state.
In the eastern Jharkand state, another landmine was detonated killing six paramilitary soldiers and two civilians.
Eight election officials were also kidnapped in Jharkand, where a number of people had been killed in clashes between the police and fighters the previous day.
There were also attacks in Bihar and Orissa.
The Maoists, who say they are fighting for the rights of poor farmers and landless labourers, have called for a boycott of the election and blocked roads to prevent officials from reaching polling stations.
Many people in India's eastern states defied the Maoists to go to the polls.
"I am aware of the threat by militants, but one can't stay at home out of fear," Monalisa Bordoloi Chakravarty said as she queued to vote in one town in Assam state.
But in Bihar, turnout was reportedly around 50 per cent, lower than most other states.
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 when the results are finally announced on May 16.
With a myriad of other parties expected to take up to 50 per cent of the 543 seats in the Lok Sabha, the final result will kick off an intense period of political horse-trading as the major players rush to form a coalition.
Exit polls are not carried out during the staggered election in order to avoid later voters being influenced.
Reporting on Thursday from Varanasi in Uttar Pradesh, the country's most populous state, Al Jazeera's Matt McClure said: "India's parliament is likely to look very different from the current one.
"The Congress party here is facing a stiff challenge from the Hindu nationalist BJP, but it is also being challenged by two smaller, regional, caste-based parties - the Samajwadi party and the Bahujan Samaj Party, who many people here have said they are considering voting for."
Singh said on Wednesday that he would be open to renewing an alliance with communist parties after the election despite an angry split last year over a civilian nuclear deal signed with the US.
The prospect of a shaky coalition of disparate allies is a turn-off for most Indian voters, with any new government likely to face national security concerns and a sharp economic slowdown after years of soaring growth.
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, which is led by the communists.
Manmohan Singh, India's prime minister and Congress party member, urged voters not to be swayed by religion or social position.
"There are certain parties in India which want to do vote politics by dividing the country on the basis of religion, community and caste. With such politics the country cannot move forward," he said on Thursday.
"We need to save ourselves from the politics that divides the society and spreads hatred."
Congress, ending a five-year period in power, has seen its main achievement - economic growth averaging more than eight per cent in recent years - hit by the global economic crisis.
|About 140 million people were eligible to vote in the first phase of India's election [AFP]
"As citizens of this country we want basic facilities for development like electricity, water, jobs for our young," Chotte Lal Singh Patel, a village elder from the outskirts of the city of Varanasi, said on Thursday.
Grassroots issues are behind the rise of regional and local groupings which have succeeded in splintering national support for the established parties by catering to small constituencies.
Rasheed Kidwai, a political analyst, said: "India needs a strong government at this stage to be able to tide us over the economic crisis in particular, besides issues like relations with Pakistan and instability elsewhere.
"But it seems increasingly likely that we're going to get a weak coalition that will probably only last two to three years."