India's Prime Minister Narendra Modi inaugurated a temple on Monday that embodies the triumph of his muscular Hindu nationalist politics, galvanising loyalists in an unofficial start to his re-election campaign this year.

Modi, in flowing golden-coloured traditional dress, unveiled the black stone idol to the deity Ram in the heart of the 50-metre temple, built on grounds where a mosque stood for centuries before it was torn down in 1992 by Hindu zealots incited by members of his party.

That demolition triggered the worst religious riots since India’s independence – killing 2,000 people, most of them Muslims – and shook the foundations of India's officially secular political order.

Outside, tens of thousands of chanting and dancing devotees waving flags, honking horns and beating drums, packed the streets of the northern town of Ayodhya, as military helicopters showered flower petals from the sky.

For Modi's ruling Bharatiya Janata Party (BJP), the opening of the Ram Mandir temple is a landmark moment in a decades-long campaign to align the country's governance with its majority faith.

"The Lord has made me an instrument to represent all the people of India," Modi said ahead of the "auspicious" opening, as he prayed at the feet of the human-sized statue, garlanded in flowers and draped in jewels.

Modi and the BJP have sought to bring the Hindu faith to the forefront of public life since sweeping to power a decade ago.

Party luminaries regularly condemn earlier eras of Islamic rule over parts of India as a time of "slavery" when their own religion was oppressed, with Ayodhya a key plank in their narrative.

Devout Hindus believe Ram, one of the most revered Hindu gods, was born in the town more than 7,000 years ago, but that the Babri mosque was built over his birthplace by a 16th-century Muslim emperor.

The BJP played an instrumental role in public campaigning that eventually led to the mosque's demolition.

The destruction presaged the rise of the BJP and Modi as unstoppable electoral juggernauts, displacing the secularist Congress party that had governed India almost without interruption since independence from Britain.

Modi's consecration of the temple alongside Hindu priests will again project him as a defender of the faith ahead of a general election expected to begin in April. (AFP)