Prime Minister Narendra Modi on Sunday launched a blistering attack on Bengal Chief Minister Mamata Banerjee, accusing her of "betraying and insulting" the people of the state who trusted she would bring about a change after the Left rule.

He also accused her of nepotism by choosing to play the limited role of "bua" (aunt) to her "bhatija" (nephew) instead of becoming "Didi" (elder sister) to the people.

Addressing a massive BJP rally at the Brigade Parade Grounds, his first in Bengal after the announcement of the dates of Assembly polls, Modi hit out at his detractors who accuse him of favouring a handful of his businessmen friends.

"You have betrayed and insulted the people of Bengal who trusted that you will be the harbinger of change after the end of the Left rule. You smashed to smithereens (chaknachoor) their hopes and dreams," he said, excoriating the TMC supremo.

The crowd at the Brigade Parade Ground on Sunday. Twitter/ @BJP4Bengal

He alleged Banerjee promoted nepotism while neglecting the people who fondly called her 'Didi'.

"Bengal chose you in the role of 'Didi' but you preferred being 'bua' to your 'bhatija'," he said.

The BJP has been accusing Banerjee of trying to install her nephew and Diamond Harbour MP Abhishek as the next chief minister.

Hitting back at rival leaders like former Congress president Rahul Gandhi and Banerjee, who often accuse him of favouring his industrialist friends, Modi said given his humble background he valued friendship.

"All 130 crore people of India are my friends, I work for them. I gave 90 lakh gas connections to my friends of Bengal. I have special affinity with tea, and the tea garden workers of Bengal are my friends for whom I have implemented a social security scheme," he said.

Modi has often spoken about how he used to sell tea at a railway station and on trains as a small boy.

He also attacked Banerjee for triggering the insider- outsider debate.

"When those believing in Marx and Lenin and a party like the TMC, an offshoot of the Congress, are parties of insiders, how the BJP, for whose foundation Syama Prasad Mookerjee was the source of inspiration, can be a party of outsiders," he said.

The prime minister said he was committed to bringing about "asol parivartan" (real change) in Bengal where all sections of people progress but nobody is appeased, and infiltration is stopped.

"Be it North Bengal or South Bengal, ordinary people or refugees....all will progress but nobody will be appeased.

Infiltration will be stopped completely," he asserted, reaffirming his commitment to the Mantra of 'Sabka Saath, Sabka Vishwas'.

Accusing the TMC government of destroying the democratic system, he alleged 'loktantra' (democracy) was replaced with 'lootantra' (systematic plunder) in the 10 years of its rule.

"Lotus is about to bloom in Bengal because of the 'kichad' (muck) created by you, Didi," he said.