AHMADABAD: At least six people have died in the worst violence to hit Narendra Modi's home state in more than a decade, police said, as the Indian prime minister appealed for calm.

Fresh communal clashes erupted on Wednesday in western India as police and paramilitary forces tried to quell riots led by members of a farming caste demanding government benefits.

Authorities imposed a curfew in at least five cities in Gujarat state on Tuesday night after mobs attacked police with stones and sticks and burned vehicles. Cellphone communications were blocked in the state's main city of Ahmadabad to stop both rumors from spreading and gangs from coordinating their movements.

Police said five people had been killed, including a father and son caught in a protesting crowd on their way home from work and then killed when police fired on the crowd on Tuesday night in Ahmadabad.

On Wednesday, two people died from police gunfire in Palanpur, and a third was killed by paramilitary fire in Mehsana, according to police officials who refused to be identified by name because they were not authorised to speak with media.

Isolated clashes between protesters and police occurred in several other cities in Gujarat, including the diamond cutting and polishing hub of Surat.

TV stations reported that police fired tear gas to disperse the crowds in some parts of the state, where Prime Minister Narendra Modi was chief minister for 12 years.

Ahmadabad's streets were otherwise deserted as schools and businesses closed after the leader of the Patidars, also known as the Patel community for the members' surname, called for a general strike to press the group's demands for the special status given to many minorities in India, guaranteeing them a share of government jobs and school places.

Patidars make up about 20 per cent of Gujarat's 63 million people and say their livelihoods based on seasonal farming and small industry have become increasingly difficult amid India's agricultural malaise and rapid economic growth marked by high inflation.

India's constitution sets out affirmative action, called reservations, for India's lowest Dalit and untouchable castes to help them overcome centuries of discrimination. Expansions over the years included several other relatively disadvantaged low caste groups.

Because reservations allow easier access to government jobs, schools and universities, they've become a huge political bargaining chip in this country of 1.2 billion people, and over the last decade several groups have led violent protests to demand that they be counted at the bottom of the country's complex, ancient system of caste hierarchies.

On Tuesday, Patel leaders led a rally attended by 500,000 community members from across Gujarat. Later, police detained the group's 22-year-old firebrand leader Hardik Patel, triggering riots.

Modi's successor as chief minister, Anandiben Patel, urged members of her own community to maintain peace. She has said giving in to the demands was impossible, because the state legally can set aside only 50 per cent of jobs and school seats for economically backward groups, and those spots are already filled by other low-caste groups.