India is set to begin the world's largest general elections on Friday, held in terrain sweeping from the icy Himalayas to humid jungles, with nearly a billion people eligible to choose 543 members of the lower house of parliament.

Opinion polls suggest an easy victory for Prime Minister Narendra Modi's Bharatiya Janata Party when the results are announced on June 4.

But more than six weeks will elapse from the time the first vote is cast on April 19 until it is counted.