Millions of people are heading to the polls in India's most populous state, in a month-long election that pits a powerful low caste leader against the ruling Congress Party with repercussions that could affect the entire country.

Analysts expect the seven-stage election to be a major national test for the ruling party, which has been hit by corruption scandals and waning support over the past few years.

The scion of the Gandhi political dynasty, Rahul Gandhi, has led the Congress Party's campaign in Uttar Pradesh in the hopes of preventing a poor showing that could weaken the party's chances nationwide in the 2014 general elections.

Meanwhile, Chief Minister Mayawati — who goes by one name — has been campaigning among the low caste voters who form her key base. She says she has improved their lives through welfare projects during her five-year term, but she also faces criticism for amassing personal wealth during her tenure.

Uttar Pradesh has a population of some 200 million people. If it were a country, it would be the world's fifth-most populous nation.