Muslims form a large chunk of the Varanasi electorate, and it was earlier believed that the community's votes may split between Kejriwal and Ajay Rai of the Congress.
Election Commission officials said that more than 50 percent of the 66 million electorate had voted in the first six hours after polling began at 7 a.m., the maximum in West Bengal.
Although the contest is intense in each of the 41 constituencies voting Monday, most attention across the country was on Varanasi where AAP leader Arvind Kejriwal claimed he was sure to defeat Modi.
"The situation has changed in the last three days, and now everyone is saying Modi is losing," Kejriwal told journalists.
Kejriwal insisted that the Varanasi battle was no more a triangular contest. "(Congress candidate) Ajai Rai does not feature anywhere. I feel it is a direct fight with Modi."
The BJP is equally confident of ensuring Modi's win by a huge margin in Varanasi, the second Lok Sabha seat from where the Gujarat chief minister is contesting besides Vadodara in his home state.
Modi, who will be India's next prime minister if he leads his BJP-led coalition to victory, Monday urged the electorate to vote in large numbers and contribute towards changing the country's future.
