Priyanka Gandhi Vadra became the latest member of India's storied Nehru-Gandhi dynasty to enter politics in January, but the boost she brings to the opposition campaign may not turn the tide against Prime Minister Narendra Modi, polls show.

After years of speculation, the charismatic Vadra joined Congress to help its leader, her brother Rahul, in general elections that begin next week, pitching the party and regional groups against Modi's Hindu nationalist-led alliance.

Congress hopes the fourth-generation siblings of a dynasty that ruled India for decades after independence from Britain in 1947 and is still revered by many will help energise its ranks and counter Modi's Bharatiya Janata Party (BJP).

See: ‘Priyanka magic’ draws thousands at debut rally

In the run-up to the election that starts on Thursday, the 47-year-old Vadra has spent hours campaigning in cars, trucks and even a boat, to woo voters in northern Uttar Pradesh, which sends more lawmakers to parliament than any other Indian state.

Reuters followed her at two roadshows where she smiled, waved, and shook hands, occasionally wading into crowds as her security detail scrambled along. Her father and grandmother, both former prime ministers, were assassinated.

Thousands of people lined the streets for several kilometres, waving Congress flags and chanting her name.

“There is support for Congress because of Priyanka,” said Mahesh Gupta, a shopkeeper in the temple town of Ayodhya, where she visited a shrine in late March.

Gupta, who referred to Vadra by her first name, as many Indians do, voted for Modi in the last election, but said he was considering Congress after seeing her campaign.

Ayodhya is at the heart of decades of tension between Hindus and minority Muslims, as Hindu groups led by the BJP have campaigned for a temple to the god-king Rama to be built on the site of a mosque razed to the ground by Hindu zealots in 1992.

Vadra, a marquee campaigner for Congress, chose Ayodhya as one of her first tours to take on the BJP in its own bastion.

Even so, in the face of the formidable political machine of the BJP which also rules the state, Congress may be unable to capitalise on her appeal, pollsters and some party leaders said.

Vadra's campaigning was getting attention for Congress it would not have got otherwise, but it did not look like the party was making gains, said Milan Vaishnav, an analyst at the Carnegie Endowment for International Peace.

“Many in Congress say the Priyanka play is more about building up the party for 2022 assembly elections and beyond,” he said, referring to state elections in Uttar Pradesh.

Last month, polling agencies CVoter and CNX separately estimated Congress would win just 4 of the 80 seats up for grabs in the state, doubling its tally since the last general election in 2014.

That year's sweep of 71 seats for the BJP paved the way for Modi's clear majority in India's 545-member lower house of parliament.

A broader poll published by the Hindu newspaper on Friday showed Modi's approval ratings across India were higher even than in 2014, when he was making a bid for power.

The poll, by the Hindu CSDS-Lokniti, showed 43 per cent of respondents wanted Modi as the next prime minister, with 24pc for Congress leader Rahul Gandhi.

Vote wisely

For years, Vadra helped manage elections for her brother and mother, former Congress president Sonia Gandhi, in their own constituencies, but was reluctant to get into politics herself.

A mother of two, she is married to businessman Robert Vadra, and has long been seen as a natural politician with strong speaking skills and an ability to easily connect with people.

One afternoon last week, her 12-car convoy sped past lush fields and small settlements, kicking up a cloud of dust before stopping at the village of Atka in the Ayodhya district.

The saree-clad Vadra jumped out of her car and settled down on the ground surrounded by a group of women, many veiled and others smiling.

“If someone doesn't work for you, how will you teach them a lesson?” she asked, imploring them to vote wisely. “Vote for those who want to work for you.”

CVoter, which has run a daily opinion poll since January, said Congress support in Uttar Pradesh has dropped after jumping 10 percentage points in the days following the news that Vadra had taken a party post.

Late in March, about 8.9pc of state voters backed Congress, a far cry from the 43.4pc supporting the BJP and the 44pc behind an alliance of two major regional parties.

However, even with Vadra's hectic campaigning, Congress is struggling to get its message of welfare to voters, party officials said.

Six voters in Uttar Pradesh said they had not heard of a Congress election promise for a programme to give India's poorest families monthly handouts of 6,000 rupees.

“They brought her in at a very wrong time,” said one Congress official, who declined to be identified because he was not authorised to speak formally to media.

A better time would have been December, just days after Congress won power in three key states, giving her more time to prepare, he added. Others in the party have said it should have been years earlier.

The BJP has dismissed Vadra's formal entry into politics as inconsequential and Modi said it only showed that for some “the family is the party”.

Vadra's office did not respond to a request from Reuters for an interview.

But Congress will seize on momentum building against the BJP, said Kamal Nath, a top Congress leader and chief minister of the central state of Madhya Pradesh.

“You have to time everything,” he told Reuters. “You don't want to peak out too fast.”