Three supporters of India's ruling right-wing party and another from a rival were killed in a gun battle in West Bengal state.

At least 18 others were wounded in clashes that broke out Saturday in the eastern state that has been on edge since Prime Minister Narendra Modi's Bharatiya Janata Party (BJP) launched an aggressive campaign to win parliamentary seats last year.

"Three of the dead were BJP workers while the other was a [regional] Trinamool party supporter," an unnamed police official told AFP news agency.

Local BJP leader Mukul Roy tweeted three BJP workers were "shot dead" in Sandeshkhali, West Bengal.

The clashes broke out over the hoisting of BJP flags and the putting up of posters, said BJP's general secretary in the state, Sayantan Basu.

"They tried to throw away our party flags and posters and when we protested, our workers were shot from point blank range," Basu was quoted as saying by Press Trust of India.

Local minister Jyotipriyo Mullick, who belongs to the Trinamool party, said one of their supporters was "hacked and shot dead by BJP workers".

"When he was on his way to attend a party meeting, he was hacked at first. When he managed to free himself, he was shot dead," Mullick told reporters in Sandeshkhali.

Rival supporters have regularly clashed in the politically volatile state where the BJP won 18 seats, up from the two it managed in 2014, en route to its massive nationwide win last month.