Congress party leaders from left, P.Chidambaram, Sonia Gandhi, Mallikarjun Kharge, Rahul Gandhi and K.C. Venugopal display copies of party’s election manifesto in New Delhi on Friday. AP

India's main opposition party Congress vowed on Friday to protect minorities — generally seen as a reference to the country's Muslims — while accelerating growth and jobs in a manifesto for an election it is widely expected to lose.

Nearly a billion Indians will vote to elect a new government in six-week-long parliamentary elections starting on April 19, the largest democratic exercise in the world.

Many analysts see Prime Minister Narendra Modi's re-election under his Hindu nationalist Bharatiya Janata Party (BJP) banner as a foregone conclusion.

Congress led India's independence struggle and dominated politics for most of the next seven decades but its secularist vision has since struggled against the BJP's appeal to members of India's majority faith.

In its manifesto, Congress promised to protect "linguistic and religious minorities." "The plurality of religions represents the history of India," it said. "History cannot be altered."

India has a long and grim history of sectarian clashes between the country's Hindu majority and Muslims, its biggest minority faith with 200 million members.

Rahul Gandhi speaks during the release of the party's manifesto in New Delhi. AFP

Party leader Rahul Gandhi — the son, grandson and great-grandson of prime ministers — said the upcoming election was "fundamentally different" from any other in India's history.

"It is between those who want to end India's constitution and democracy and those who want to save it," he said.

The Congress manifesto, titled a "justice document", offered "concrete guarantees unlike Modi's empty promises," said lawmaker and lead author P Chidambaram.

The party has promised to address India's "massive unemployment" on a "war footing", adding that it would earmark half of all government jobs for women.

Priyanka Gandhi Vadra gestures as she arrives to attend the release of the party's manifesto in New Delhi. AFP

Young people voted for Modi in droves when he was first elected a decade ago after he said he would create 10 million jobs a year. But a recent International Labour Organisation (ILO) report warned that India was hamstrung by a "grim" crisis, with unemployment on the rise.

Congress proposed an unconditional annual cash transfer of Rs100,000 ($1,200) "to every poor Indian family," without precisely defining who would qualify.

The BJP is yet to publish its own manifesto.