State polls

UP: 403 seats, 5,553 candidates, 99 million voters Uttaranchal: 70 seats, over 900 candidates, 5.2 million voters Manipur: 60 seats, 377 candidates, 1.47 million voters

In the past, elections in UP have been marred by voter intimidation and violence and the authorities seem determined to clamp down.

Nearly 100 million voters are eligible to vote for over 5,000 candidates.

Several candidates have criminal records and India's independent election commission is using video teams to monitor their movements.

Voters are also using electronic voting machines for the first time in an attempt to clamp down on electoral malpractices.

"Earlier the rough and tough guys would just come and stamp all the ballot papers. Now each voter has to punch a button," UP Home Secretary, Naresh Dayal, told Reuters.

BJP's tough ask

Correspondents say as the outgoing administration, the BJP faces a tough task.

The prime minister has been campaigning hard

As well as being India's most populous state, UP is also one of its poorest and many people, especially in rural areas, are angry about political promises of development which they say have not been realised.

But Uttar Pradesh is often seen as a litmus test of national opinion and defeat could send shockwaves through the fragile BJP-led national coalition in Delhi.

In pre-election campaigning, BJP leaders focused on their tough stance on Pakistan since the bombing of India's parliament in mid-December.

But the BBC's Jill McGivering, who is in UP, says it is uncertain if that appeal to a sense of Hindu nationalism will succeed in helping them to keep control of this key state.

Manipur

Voting is also taking place in the remote north-eastern state of Manipur, which was rocked by violence last year.

Some 240 candidates are contesting 40 seats out of a total 66 - the remaining go to the polls on 21 February.

There have been some reports of irregularities.

More than 20,000 soldiers and policemen have been deployed to prevent violence by rival political parties as well as separatist groups.

A moderate turnout has also been reported in Uttaranchal. Electoral officials told the BBC that voting was peaceful.

Voting in a fourth state, Punjab, took place on Wednesday. Final results are expected on 24 February.