Vote counting in key Indian state elections was underway Monday under tight security, with the focus on West Bengal, where Prime Minister Narendra Modi's party appeared set for victory.

And in the southern state of Tamil Nadu, veteran politician MK Stalin was trailing, challenged by a political debutante -- film star C Joseph Vijay.

Elections in five states and territories took place in April and May, with Modi's Bharatiya Janata Party (BJP), the ruling party in the national parliament, seeking to make inroads into opposition-held states.

In West Bengal, the Hindu-nationalist BJP waged an aggressive bid to dislodge Chief Minister Mamata Banerjee, the firebrand leader of the All India Trinamool Congress (TMC), in power in the state of 100 million people since 2011.