People stand in queues to cast their votes at a polling booth in Nandigram, India, on Thursday. Bikas Das/AP

Prime Minister Narendra Modi's Hindu-nationalist party and the firebrand leader of West Bengal, Mamata Banerjee, are caught up in a fierce battle for the eastern state renowned for its high levels of political violence and murders.

Prime Minister Narendra Modi speaks during a rally. File photo

Campaigning in the town of Nandigram has been particularly intense, with 66-year-old Banerjee — one of Modi's fiercest critics — contesting the seat against a former confidante who defected to Modi's Bharatiya Janata Party (BJP) last year.

Hundreds of supporters of Banerjee's Trinamool Congress party and the BJP clashed outside polling stations in Nandigram on Thursday, despite an Election Commission banned on gatherings of more than four people.

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Police told AFP a worker for Banerjee's Trinamool Congress party (TMC) was "hacked to death" early Thursday with three BJP supporters detained for questioning.

A BJP worker also allegedly killed himself after he was threatened by TMC supporters, police said, citing a complaint filed by his family.

A woman adjusts her facemark as she stands in queue with others to cast their votes in Nandigram, India. AP

Despite the outbreaks of violence, thousands of people queued at hotly contested Nandigram's polling stations to cast their vote.

The West Bengal polls are being held over eight phases amid tight security and conclude on April 29. The second phase of voting involves 30 constituencies including Nandigram.

In another district, West Midnapore, police said a TMC camp was raided by BJP supporters, with party flags ripped up and vehicles damaged.

"BJP supporters came in with force and threw crude bombs and rocks," a police spokesman told AFP.

The BJP has been seeking to expand its power at the state level beyond its Hindi-speaking northern heartlands.

West Bengal, home to more than 90 million people with some 73 million eligible to vote, has so far eluded the BJP.

The results of the West Bengal poll will be announced by the Electoral Commission on May 2, alongside several other state and territory elections in Assam, Kerala, Tamil Nadu and Puducherry.

The second out of three phases of polling in the northeastern state of Assam -- where the BJP is looking to hold on to power after winning for the first time in 2016 -- also commenced on Thursday.