Congress party president Rahul Gandhi. File Photo

India's main opposition Congress party has told its workers not to lose heart and to remain vigilant at vote-count centres after exit polls predicted a clear election victory for Prime Minister Narendra Modi.

The counting of votes cast in the seven-phase general election will take place on Thursday, with the result expected later that day.

Modi's ruling coalition is projected to win between 339 and 365 seats in the 545-member lower house of parliament with a Congress-led opposition alliance getting only 77 to 108, an exit poll from India Today Axis showed on Sunday.

The ruling alliance, led by Modi's Bharatiya Janata Party (BJP), seems assured of victory and will meet in New Delhi later on Tuesday to discuss a new government.

But exit polls in India have proved misleading before and Congress general secretary Priyanka Gandhi Vadra, the younger sister of party president Rahul Gandhi, urged party workers to ignore them, and to keep the faith.

"Don't let rumours and exit polls discourage you. This is being spread to break your determination," she said in an audio message late on Monday.

"This has further raised the need for you to remain alert. Please keep vigil outside strongrooms and counting centres. We are confident that our combined efforts will bear fruit," she said, referring to centres where electronic voting machines are kept.

The two Gandhis are members of the latest generation of the Nehru-Gandhi dynasty to aspire to govern India.

The staggered general election, billed as the world's biggest democratic exercise with some 900 million eligible voters, began on April 11 and finished on Sunday.

The BJP says it is confident the final results will reflect the exit polls. On Tuesday afternoon, workers decorated the party's headquarters in Delhi with lights and flags and put up big tents in anticipation of the celebrations to come.