In the early morning, before the sun has risen above the tenements and temples, there is noise, music, banter, and occasional scuffles in the narrow streets leading down to the Ganges. Men shout, laugh, bang drums, and hand out pamphlets. Rickshaws swerve, the police watch and pilgrims file past unconcerned, eyes only for the slick surface of the river itself.

Tourist brochures have long described Varanasi, India's holiest city and one of the oldest continually inhabited settlements in the world, as "eternal" or "unchanging". But this weekend such adjectives are misplaced. The noisy groups in the streets are volunteers who have come to take part in the final battle of the long, bad-tempered, bitter but extraordinary Indian elections. Staged over six weeks to allow the redeployment of security personnel, the polls finally close on Monday evening. By then, more than 800m will have had the chance to vote at 930,000 polling booths all set up within walking distance of their homes. Local analysts have repeatedly described the election as "historic."

"This is an election where there are stark choices to be made in a way not seen for decades. There are big social forces interacting - and the beginnings of a new national mood," said Ashok Malik, a centre-right commentator.

Though the election has been fought primarily on issues of economic development, other darker issues such as religion and caste have dominated in the latter stages of the campaign.

And if the contest is a battle of different visions of India, it is also one of very different styles and strategies. New forces unleashed by rapid urbanisation, a booming media, massive internal migration, growing literacy and prosperity are forcing politicians to adapt fast or fail. The battle in Varanasi, in the vast and poor northern state of Uttar Pradesh, unites all these various elements and reveals new ones. Some say it offers a glimpse of a transformed political landscape.

"It's the glint of a new wave democracy, where volunteers are swept into the eye of the poll storm, turning them into leaders and activists, instigators and disrupters and most importantly, Citizen India,' wrote Vrinda Gopinath, in the Mail Today newspaper last week.

In Varanasi, it is the newly formed Aam Admi (Common man) party, which has the greatest presence on the streets. Led by Arvind Kejriwal, a 45-year-old tax inspector turned activist, the AAP has mobilised around 2,000 volunteers from all over India who distribute pamphlets and caps, wave banners, go door to door and organise rubbish collections. Kejriwal, who came to public attention as a leader of a nationwide anti-corruption protest three years ago and briefly ran the capital Delhi after a surprise success in local polls last year, has refused the small army of bodyguards usually deployed to protect politicians and other elements of Indians call ‚"VIP culture". The party office is a modest and very overcrowded suburban house. On Friday evening, he led a 'roadshow' through Varanasi, sitting on the top of a jeep, surrounded only by excited partyworkers and preceded by hundreds of teenagers on bicycles and scooters waving brooms, the AAP symbol.

Ashutosh, an AAP parliamentary candidate who stood in Delhi before coming to Varanasi to help the campaign, said a "revolution" was happening. "Since the 1970s politics has been about money power, muscle power and dynasty ... We are trying to turn that paradigm around. We have tried to reach out to every individual and empower them," said the former TV journalist who goes by one name.

Even if the AAP is unlikely to take more than a few seats nationally, its entry into the contest in Varanasi has turned a straightforward duel between the centre left Congress party, which has ruled India since 2004, and the Hindu nationalist Bharatiya Janata Party (BJP), the main national opposition, into a chaotic melee.

Leaders from the BJP - which won in Varanasi at five of the last six elections - contemptuously dismissed Kejriwal's efforts. "No challenge at all," said BJP deputy leader Ravi Shankar Prasad. In turn, AAP officials said Prasad was "arrogant and complacent."

The BJP candidate in the city is Narendra Modi, the 63-year-old political outsider who has dominated this campaign. Modi is one of the most polarising Indian leaders for decades: Supporters say he is an effective, honest, dynamic leader with administrative experience who will boost India's faltering economy. Critics say he is a dangerous authoritarian who is prejudiced against the country's 150m strong Muslim minority.

"The people of the country are yearning to make Narendra Modi their prime minister and the people of Varanasi are more than keen that he should be their MP," said Prasad.

The BJP campaign contrasts dramatically with that of the AAP. A huge advertising campaign and blanket TV coverage of a series of immense rallies have made Modi's bearded face, his pledge of development and his call for for the 1.25bn inhabitants of this crowded, fast-changing and troubled nation to put "India first" ubiquitous. A study last week found Modi had received more than seven times the media attention of his nearest rival. BJP officials say they designed their strategy after studying the Labour Party's successful campaign in the UK in 1997.

There has also been a huge social media campaign, conducted by volunteers from across India such as Pradeep Singh, an IT specialist who has taken time off from his job with a major multinational.

Born in Varanasi, Singh said he had been "pained" by the lack of development of the city, with its rutted roads, power cuts, filth and open sewers. His own attempt to set up a business in his hometown ended after extortion attempts. Modi would not just bring development and security, Singh said, but would protect the culture of the city, and India. "I am a Hindu nationalist. I proudly say I am from Varanasi. We need basic amenities – jobs, roads, sanitation – but the cultural wrapping of Varanasi should remain," said Singh, 25.

This combination of identity and economic development is hugely powerful. Indians' expectations have been raised by successive years of growth and a booming media. Formerly distinct divides between rural and urban communities have blurred. But many have been disappointed as growth has faltered and opportunity faded. There is a deep desire for radical solutions to allow the resumption of India's advance towards prosperity and stability.

"There is a lot of anger. There is a comparison not with some mythical past but with three years ago and [Modi] has a great narrative: he has come from humble origins, is angry and tough, has created jobs, he is honest, so people think 'let's give him a go,'" said Malik, the commentator.

Though successive opinion polls have put Modi well ahead of the Congress party, which has dominated Indian politics for decades, the Congress candidate in Varanasi is confident that the city's voters will back him. Ajay Rai is perhaps the most traditional of all those battling for this seat. A political survivor who has contested seven elections, Rai has serious criminal charges against him - including attempted murder and gangsterism. This is not unusual in India, where according to recent research, nearly a fifth of candidates are accused of serious offences. Rai told the Guardian the accusations against him were "politically motivated".

Rai and his aides say voters relate to him as a "local boy". But bloc loyalties of castes and religious communities are key to Rai's strategy. Congress has long counted on the votes of dalits, those at the bottom of the caste hierarchy, and Muslims, who comprise nearly a quarter of voters in this constituency. The support of a local Muslim strongman and independent politician, currently in jail on organised crime charges, is also expected to bring a welcome boost.

This may be a miscalculation. In Ardali Bazaar, a Muslim neighbourhood, voters appear split. Mohammed Tahseen Razza, a teacher in an Islamic school, said voting Congress was important to "stop Modi" and prevent a repeat of sectarian violence in Gujarat in 2002 in which 1,000 people, largely Muslim, died. But others pledged support to the new Aam Admi Party, out of anger at political corruption and deal-making.

Down on the stepped jetties which line the holy and heavily polluted river, groups of BJP and AAP activists shouted slogans. If the three-sided battle in Varanasi is almost over, the changes evident here are likely to outlast the mandate of the victor.

"I never thought I would get into politics but here I am spending my savings to do this in the interests of my country," said Joginder Singh Rana, who had left his pump workshop in Delhi to spend a week campaigning for the AAP.

Nearby stood Ashok Chaudhury, a 54-year-old farmer from the central state of Chhattisgarh and a first-time volunteer campaigner for the BJP. "If you look at this city, whether politics or religion, it represents the beginning. When a message emanates from Varanasi, it reverberates around the entire country," he said.