The 73-year-old leader is widely expected to win a third term when the poll concludes early next month, thanks in large part to his aggressive championing of India's majority Hindu faith.
"My vote is for the BJP and Modi," said Deepak Mahajan, 42, who works in banking. "There is no other choice if you care about the future of the economy and business. I have always voted this way."
Big conglomerates have bestowed upon Modi's ruling Bharatiya Janata Party (BJP) a campaign war chest that dwarfs its rivals, while Bollywood stars have backed its ideological commitment to more closely align the country's majority religion and its politics.
Data published this year showed that the BJP was by far the single biggest beneficiary of electoral bonds, a contentious political donation tool since ruled illegal by India's top court.
Leading companies and wealthy businesspeople gave the party $730 million, accounting for just under half of all donations made under the scheme in the past five years.
Conglomerate owners support Modi's government because it caters to the needs of India's "existing oligarchic business elite", Deepanshu Mohan of OP Jindal Global University told AFP.
Lower corporate tax rates, less red tape and a reduction in "municipal regulatory corruption" have also helped Modi win the affection of corporate titans, he said.
N. Chandrasekaran, the chairman of Tata Sons, a sprawling Indian conglomerate with interests ranging from cars and software to salt and tea, cast his ballot at a polling station in an upper-class Mumbai neighbourhood.
"It's a great privilege to have the opportunity to vote," he told reporters. "And I would request all Mumbaikars to come and exercise their franchise and vote today."
Bollywood stars
It is Modi's cultivated image as a champion of the Hindu faith, rather than an economy still characterised by widespread unemployment and income inequality, that has undergirded his enduring popularity with the wider public.
This year in the town of Ayodhya, he presided over the inauguration of a grand temple to the deity Ram, built on the grounds of a centuries-old mosque razed by Hindu zealots in 1992.
Construction of the temple fulfilled a longstanding demand of Hindu activists and was widely celebrated across the country with back-to-back television coverage and street parties.
The ceremony was attended by hundreds of eminent Indians including Asia's richest man Mukesh Ambani, whose family donated $300,000 to the temple's trust.
Also present were cricket star and Mumbai native Sachin Tendulkar along with actor Amitabh Bachchan -- the single most famous product of Bollywood, as the financial hub's film industry is known.
Numerous screen stars have established themselves as vocal champions of Modi's administration since he was swept to office a decade ago.
Former soap actress Smriti Irani is one of the government's most recognised ministers and beat India's most prominent opposition leader Rahul Gandhi in the contest for her current parliamentary seat in 2019.
Filmmakers have also produced several provocative and ideologically charged films to match the ruling party's sectarian messaging, which critics say deliberately maligns India's 200-million-plus Muslim minority.
Last year's "Kerala Story" was heavily promoted by the BJP but condemned elsewhere for falsely claiming thousands of Hindu women had been brainwashed by Muslims to join the Islamic State group.
- Heatwave returns -
India's election is conducted in seven phases over six weeks to ease the immense logistical burden of staging the democratic exercise in the world's most populous country.
The fifth round is taking place as parts of India endure their second heatwave in three weeks, after much of the continent suffered searing temperatures in April.
Turnout is down several percentage points from the last national poll in 2019, with analysts blaming widespread expectations of a Modi victory as well as hotter-than-average temperatures heading into the Indian summer.
Tens of millions of people in Uttar Pradesh, West Bengal, Maharashtra and Jharkhand states are voting under heatwave conditions and temperatures expected to hit 40 degrees Celsius (104 degrees Fahrenheit) on Monday.
Scientific research shows climate change is causing heatwaves to become longer, more frequent and more intense, with Asia warming faster than the global average.
More than 968 million people are eligible to vote in the Indian election, with the final round of polling on June 1 and results expected three days later.
