Half a million people march against Modi in Kolkata

India's opposition parties drew half a million supporters to Kolkata's streets on Saturday (19) for the largest show of force yet against prime minister Narendra Modi as a national election looms.

Police in the eastern city said 500,000 people turned out for the massive "Unite India" rally, which saw leaders from across the opposition spectrum rail against Modi and his ruling Hindu nationalist party.

Speeches were beamed on 20 giant screens to a sea of spectators waving the national tricolour flag and the banners of India's myriad opposition movements. Police said 5,000 officers were on standby for security.

"The Modi government is past its expiry date," said Mamata Banerjee, the chief minister of West Bengal state, from an enormous raised platform.

Her government, which organised the rally, had suggested four million would attend but Kolkata Police Chief Rajeev Kumar said 500,000 showed up.

Modi, who was inspecting military hardware in Gujarat state on Saturday, accused the opposition of acting in self interest.

"The alliance is not against me, it's against India," he said, as quoted by the Hindustan Times newspaper.

The rally comes as hundreds of millions of Indians prepare to go to polls expected in April and May, the world's largest democratic exercise.

Modi -- the Bharatiya Janata Party (BJP) leader who won a landslide victory in 2014 -- is seeking another term, and remains hugely popular.

But he faces rising discontentment over unemployment and economic inequality. The BJP suffered a rare reverse in December when it lost three key state elections to Congress, the main opposition party.

Its leader, Rahul Gandhi, did not attend the rally but sent party representatives. His mother Sonia Gandhi, the party's former president, said it was "an important attempt to galvanise leaders to fight the Modi government".

Speakers from India's myriad state, regional and caste-based parties urged voters from the pulpit to unite against the prime minister and his BJP.

"Narendra Modi is a publicity PM, we need a performing PM," said Chandrababu Naidu, chief minister of the southern state of Andhra Pradesh.

H.D Deve Gowda, who was briefly prime minister in the 1990s, said regional parties were powerful but "cannot save India without uniting".

The opposition has not allied in a formal bloc, but some state outfits have joined forces as the election draws nearer.

This month two regional parties that were former bitter rivals in Uttar Pradesh -- India's most populous state -- announced an unlikely alliance to challenge Modi.