Three supporters of India's ruling right-wing party and another from a rival regional party have been killed in a gun battle in West Bengal state, police and a local politician said on Sunday.

At least 18 others were injured in the clashes that broke out on 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," a police official told AFP.

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

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

Modi's party won a massive 303 seats in the national parliament, increasing its previous tally of 282 seats in 2014.

The Trinamool Congress party — which has its stronghold in West Bengal and is led by the firebrand Mamata Banerjee, accuses the BJP of fomenting trouble in the state.

The latest clashes broke out over the hoisting of BJP flags and the putting up of posters, said the 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 the Press Trust of India (PTI).

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.

West Bengal has witnessed some of the most violent feuds between rival parties. Last month, a BJP supporter was shot dead in state capital Kolkata and a car belonging to a Trinamool member was pelted with rocks.

Last year, a BJP worker was killed and his body was hanged from a tree.

Modi has called the killings "shameful and anti-democratic".