India has elected a new president from the bottom of the country's Hindu caste system, only the second time since independence a head of state has been chosen from the marginalised group.

Ram Nath Kovind, 71, a Dalit leader backed by India's ruling Bharatiya Janata Party (BJP), won 65.6 per cent of the votes, defeating Meira Kumar, the opposition Congress party's nominee, the Election Commission said.

Shortly after his victory was announced, Kovind said he was aware of the great responsibilities of his post, adding that "it was a very emotional moment" for him.

"I never thought that I would become president. It was never my goal," he said, and called his election a "symbol of the greatness of Indian democracy".

OPINION: How the BJP has come to dominate lower-caste politics

The president is chosen by an electoral college of both houses of parliament and state assemblies, and the BJP and its allies had a clear advantage.

While the president is the head of the state, executive powers are vested in the prime minister.

India has had a Dalit as president before in KR Narayanan, who held the country's highest office from 1997 to 2002.

But Kovind's win makes him the first president aligned to the Rashtriya Swayamsevak Sangh (RSS), a Hindu revivalist volunteer group which is the ideological fountainhead of the BJP.

Modi's message

Narendra Modi, India's prime minister, lauded both candidates, tweeting that Kumar's campaign "was in spirit of the democratic ethos & values we all are proud of".

Modi posted a photograph of him and Kovind from two decades ago, writing on Twitter: "20 years ago and the present ... always been a privilege to know you, President Elect."

Analysts said the election of Kovind would help Modi to tighten his grip on power and accrue political capital by sending an important message to the Dalits, a long-disdained electoral group once known as "untouchables".

Kovind, a lawyer, was born into a humble farmer's family in Uttar Pradesh, a northern state that is also the country's most populous.

On Thursday, Kovind noted that it had been raining in New Delhi since the morning, and the monsoon season reminded him of his childhood and their village home built of mud walls and a roof that leaked.

As he and his siblings huddled close to the walls, all they could do was wait for the rain to stop, he recalled.

"Today there are so many Ram Nath Kovinds in the country who are getting drenched in the rain right now, farming, working as labourers, toiling away for one meal in the evening," he said.

"I want to tell them that Ram Nath Kovind from Paraukh village is going to the presidential palace as their representative."

Kovind has been a member of the Rajya Sabha, or parliament's house of elders, held various posts within the BJP and was governor of eastern Bihar state.

Kovind is scheduled to take the oath of office on July 25.

He will succeed Pranab Mukherjee, a veteran politician from the Congress party, who completes his five-year term on July 24.

The president has an important role to play when elections produce hung parliaments, state governments are dissolved and during other political crises.