"Only the people and nobody is the big boss of this country... Only democracy is the big boss of this country," Mamata Banerjee told reporters from the site where she has been protesting since Sunday. She added: "It is not my victory alone. It is a victory of the constitution, a victory of Save India."

The CBI told the Supreme Court that it believed the Kolkata police chief, who led a Special Investigation Team into the Saradha and Rose Valley chit fund scams allegedly involving members of Mamata Banerjee's Trinamool Congress, had "doctored evidence" and shielded the accused.

The CBI went to the Supreme Court on Monday, after the CBI team that arrived at Rajeev Kumar's Kolkata home was blocked by the police, bundled into buses and detained.

Shortly after, a furious Mamata Banerjee launched an indefinite sit-in to protest against the move against her police chief, calling it a "constitutional breakdown".

"They wanted to arrest him. They went to his house on a secret operation, without any notice. That court said 'no arrest', we are so obliged. It will strengthen the morale of the officers," Mamata Banerjee said on the court order.

The Chief Minister called her protest "not an individual fight but a Jan Andolan (mass movement)". "(Prime Minister Narendra) Modi will lose in 2019...They are interfering with everything. It made my heart cry. I have digested all the injustice for too long," she said in a little speech peppered with dramatic pronouncements and even some lines from Lata Mangeshkar's iconic "Ae Mere Vatan Ke Logon".

Asked whether she would continue her protest, she said: "I will not decide in a hurry. So many opposition leaders are coming...Today Chandrababu Naidu is coming. We are not fighting alone."

Mr Naidu is the third opposition leader to make a beeline for Kolkata after Bihar leader Tejashwi Yadav and DMK's Kanimozhi. Coming out in Mamata Banerjee's support, opposition leaders have called it a larger campaign against the "trampling of democracy and institutions by the Modi government".

Congress president Rahul Gandhi, Aam Aadmi Party's Arvind Kejriwal, Samajwadi Party chief Akhilesh Yadav, BSP leader Mayawati and RJD's Tejashwi Yadav are among the leaders who have pledged support to the Bengal chief minister.