At least eight people were killed in northern India Sunday after clashes broke out at a farmers' protest, officials told local media, in a deadly escalation of their year-long campaign against controversial agriculture laws.

The farmers had gathered for a demonstration in Uttar Pradesh state's Lakhimpur Kheri district, where the junior home affairs minister Ajay Mishra and the state's deputy chief minister Keshav Prasad Maurya had been due to visit.

Chaotic scenes then broke out around vehicles reportedly part of the Mishra convoy.

"Eight persons died in today's Lakhimpur incident. Out of the eight, four were farmers and the remaining four were others who were in the vehicles," Uttar Pradesh director general of police Mukul Goel told television news channel CNN-News18.

Farmer groups claimed that Mishra's son had been in a car in the minister's convoy, or was driving it, when the vehicle ran over four protesters, killing them.

Angry demonstrators then set the cars on fire, and four more people were killed in the ensuing violence, according to early reports from farmers at the protest.

Video shared on social media purportedly from the protest showed bloodied farmers and cars going up in flames.

But Mishra denied the claims, telling local media the demonstrators had attacked the convoy and killed three workers from the Bharatiya Janata Party -- the ruling party at the national level and in Uttar Pradesh -- and one driver.

Uttar Pradesh Chief Minister Yogi Adityanath called the incident "very sad and unfortunate" as he appealed for calm.

"Before jumping to any conclusions, please wait for the ongoing investigation and the action thereafter," he tweeted late Sunday in Hindi.

Internet services in the area were cut, and roads to Uttar Pradesh state capital Lucknow were closed to quell further outbreaks of violence, local media reported.

Opposition leaders and farmer union chiefs said they were heading to Lakhimpur Kheri.

Farmers last week marked the first anniversary of the president's assent of the laws deregulating the agriculture sector, which has long been a political minefield and employs some two-thirds of India's 1.3 billion population.

Prime Minister Narendra Modi's government says the industry is massively inefficient and in need of reform. But protesters fear the changes will leave them at the mercy of big corporations.

Tens of thousands of farmers have been camped out on the borders of India's capital New Delhi since late November in one of the biggest challenges to Modi's government.

The incident came ahead of crucial elections next year in Uttar Pradesh, India's most populous state and a key source of votes for the BJP.