Under blazing heat, more than 34 million of 172 million voters exercised their franchise in the first five hours of balloting for 137 constituencies in 11 states where 1,278 hopefuls are in the fray, officials said.

All eyes were on main opposition leader Sonia Gandhi and son Rahul, 33, contesting seats in India's most vote-rich state, Uttar Pradesh in the north.

Rahul, the heir apparent of the dynasty that included India's first prime minister Jawaharlal Nehru, predicted he would win his family seat of Amethi with a "record margin."

"There is a great response and we hope to win with a good majority," said his sister Priyanka Gandhi Vadra, 32, who is not running but is seen by many as a charismatic face for the 119-year-old Congress party.

"You know, 300,000 votes just don't come like that," Priyanka said of her 57-year-old mother's victory margin in the last national election in 1999.

"But five years ago the (Congress) organisation was weak and we have worked and strengthened it and now we are hopeful that things will be in our favour," she said.

Exit polls since voting began April 20 have shown a lead for Prime Minister Atal Behari Vajpayee's coalition, but by a slimmer margin than predicted before the start of the election which ends May 10.

Vajpayee agreed the polls could no longer be seen as smooth sailing for his Hindu nationalist Bharatiya Janata Party (BJP) which called the vote early hoping to cash in on strong economic growth and a peace process with Pakistan.

Voting is being watched closely in Uttar Pradesh, which returns 80 MPs to the 545-seat parliament with regional parties expected to outperform the two main adversaries.