India's political rivals were set to hold rallies Sunday on the eve of the world's biggest election, as frontrunner for premier Narendra Modi and his Hindu nationalists battled accusations of stoking religious tensions to win votes.

Rahul Gandhi will take to the stage in New Delhi and neighbouring Haryana state to implore voters to stick with his ruling Congress party, which is tipped to suffer a crushing defeat in the marathon six-week ballot which starts Monday.

Voting will kick off in the two remote northeastern states of Assam and Tripura, before spreading across the country of 814 million eligible voters in a staggered process. Results are due on May 16.

"Congress is the only party that has resonance in every nook and cranny of India," senior party spokesman Abhishek Manu Singhvi told AFP.

He described Gandhi, the scion of India's most famous political dynasty and frontman for the Congress campaign, as a "superstar campaigner" who would return them to power.

Arch-rival Modi, a Hindu hardliner tainted by association with religious riots, is holding rallies on Sunday in the battleground state of Uttar Pradesh where he has been campaigning on a pledge of reviving the country's ailing economy.

But in the last days of the campaign a row erupted along religious lines, with Modi's right-hand man accused of stoking tensions against Muslims, who at 13 percent of the population are the country's largest religious minority.

Amit Shah reportedly told Hindu voters to seek "revenge" at the ballot box while speaking in a part of Uttar Pradesh hit by Hindu-Muslim violence last year that left some 50 people dead.

"This election is about voting out the government that protects and gives compensation to those who killed Hindus," Shah reportedly said on Friday.

Congress has asked the Election Commission to order Shah's arrest and ban him from campaigning, with a party official accusing Modi's Bharatiya Janata Party (BJP) of making "horrible" statements and "creating animosity between communities."

The election commission has declined to comment.

But Arvind Kejriwal, from the anti-corruption Aam Aadmi or Common Man Party, accused Modi Saturday of "politics of hatred".

The BJP said Shah's comments had been taken out of context and accused Congress of hypocrisy.

"The Congress should be ashamed for that challenge to the EC. They themselves are asking for votes in the name of religion," BJP spokeswoman Nirmala Sitharaman told AFP.

Modi, widely tipped in opinion polls to win the elections, has focused his campaign on economic reform and creating jobs, largely steering clear of promoting any Hindu nationalist agenda.

But he has been tainted by religious riots in 2002 in the western state of Gujarat which he has governed since 2001. The riots there killed more than 1,000 people, mostly Muslims. He has been cleared of any personal wrongdoing.