Voting in the world’s largest democratic contest will begin on 11 April and continue for the next six weeks, India’s electoral commission has said in an announcement that signals the formal start of campaigning.

Polling booths will be shuttled around the country – by camel across the Rajasthan desert, on foot in the Himalayas and by speedboat in the Andaman Islands – for an election held in seven phases ending on 19 May. The ballots of up to 900 million eligible voters will be counted four days later.

Conducting India’s massive election is made more difficult by a law demanding that no voter need travel further than two kilometres to find a polling place, as well as the need to deploy federal police to secure the ballots, with local law enforcement regarded as easier to compromise.

The announcement of the dates means the government is officially in caretaker mode and unable to announce policies or advertise new ones with public money. The electoral commission has cautioned parties not to use soldiers in their advertisements in the wake of renewed clashes between India and Pakistan in recent weeks.

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Narendra Modi, India’s most powerful prime minister in generations, will seek to replicate his party’s majority victory in 2014 – the first in a quarter of a century – against a motley coalition of regional opposition leaders who argue he has become too authoritarian.

The poll is seen as a referendum on the lavish promises Modi has made since 2014, including to create millions of jobs and improve the incomes of agricultural workers, who still make up nearly half the country’s workforce. Surveys suggest the government has lagged on both, but Modi retains an image as a tireless, corruption-free leader and voters may reward him for trying.

“Every election has impact but this one is exceptional in its importance,” said Sandeep Shastri, the pro-vice-chancellor of Jain University in Bangalore and a political scientist.

He said Modi’s Hindu nationalist government had sought to redefine the very idea of India away from its original casting as a secular republic. Another decisive win would be a green light from voters for this new vision, he said.

Modi’s party lost three state elections in December, shattering his aura of invincibility and raising the possibility that he could lose or be forced to assemble a governing coalition with minor parties. But a recent airstrike in Pakistan, and the successful repatriation of a captured Indian pilot, have created a nationalist tide across the country that could lift his prospects.

“I hope this election witnesses a historic turnout. I particularly call upon first-time voters to vote in record numbers,” Modi tweeted.

A nationwide opinion poll released on Sunday suggested that his coalition could win 264 seats in the election, compared with 141 for the Congress party-led opposition alliance. A total of 543 seats are up for grabs in the election.