Narendra Modi's landslide victory in India's polls has swept aside the long-dominant Congress party and left many of the most high-profile politicians clinging on for dear life after staggering electoral losses.

Modi's campaigners hailed the tidal wave of support for the Hindu nationalist who demolished rivals ranging from India's top low-caste politician to its most famous anti-corruption activist and a widely admired chief minister.

Nitish Kumar, former chief minister of Bihar, whose government was feted for engineering a turnaround in the once crime-wracked state, resigned after his party was decimated.

Kumar's Janata Dal (United) party won just two seats while Modi's Bharatiya Janata Party (BJP) swept the state, one of the country's most populous and poorest, taking 22.

Political analyst Paranjoy Guha Thakurta described the result as an "all-India tsunami in favour of the BJP," signifying that most people voted "for a change at the centre, ignoring the otherwise strong track record of regional leaders like Nitish Kumar."

With the exception of a handful of states in southern and eastern India, which have long lacked a significant Congress or BJP presence, the anti-incumbent vote went to Modi, Thakurta said.

Kumar's loss at the hands of former BJP allies came less than a year after he cut ties with the party over its decision to field Modi, a popular but divisive figure, as a prime ministerial candidate.

He said Modi's role as chief minister of western Gujarat state during religious riots in 2002 would alienate voters. More than 1,000 people -- mainly Muslims -- were killed in the clashes.

- Caste-focused parties lose out -

The Modi landslide also buried other rivals, including "Dalit Queen" Mayawati, a former chief minister of Uttar Pradesh state and champion of India's low-caste Dalit community previously known as "untouchables". Her Bahujan Samaj Party won no seats in the electorally pivotal state.

Moreover, Modi's success at painting himself as an unifying leader left scant room for opponents, who traditionally relied on votes from specific castes, communities and religions.

B.G. Verghese, of the New Delhi-based Centre for Policy Research, said "Modi first played the orthodox Hindu card but later changed gears, appealing to moderates as well as lower-caste Hindus, many of whom switched loyalties and voted for him."

The gamble paid off spectacularly in Uttar Pradesh, where the BJP increased its 2009 tally sevenfold, winning 71 of 80 seats and isolating usually dominant caste-focused regional parties.

Besides Mayawati, ex-wrestler Mulayam Singh Yadav's Samajwadi Party, which has relied on rural, low-caste votes, also saw its strength plummet.

Sunil Khilnani, director of King's College London's India Institute, likened the impact to "a democratic asteroid that wiped out many old habits".

"We enter a new, less predictable phase of Indian democracy, as more citizens slip loose from their caste, religious or political traditions to vote as individuals", Khilnani wrote in The Times of India.

- Soul searching for Congress -

The Modi juggernaut flattened old and new parties alike -- from the Congress, which traces its history to the 19th century, to the upstart Aam Aadmi (Common Man) Party, led by anti-corruption activist Arvind Kejriwal.

The results plunged the Congress into its worst crisis in years, leaving party leaders reeling after their seat count slid to 44 from 206 in 2009.

The Congress campaign targeted Modi's controversial past, but his economic record in Gujarat, which boomed during his stint as chief minister, won over voters. Millions approved of his pledge to reproduce those policies at the national level and revive the ailing economy.

Verghese said Congress's failure underlined the party's urgent need to look beyond the Nehru-Gandhi family, which has produced three premiers but whose scion, 43-year-old Rahul Gandhi, failed to convince voters he was fit to lead India.

"Rahul Gandhi is an absolute liability, the sooner he's discarded the better it is for the party," the analyst added.

And Kejriwal, whose early success at targeting young Indians frustrated over unemployment and corruption saw him become Delhi chief minister, also fell victim to the BJP blitz.

Commentators said the Aam Aadmi leader, who led rousing rallies against graft for months before entering politics in November 2012, overstretched himself when he took on Modi in a high-stakes battle for a seat in the Hindu holy city of Varanasi.

"Kejriwal understood there's a new-generation Indian whose time had come, but he didn't have Modi's political acumen," said Verghese.