A Muslim man has died after he was attacked by hundreds of vigilantes while transporting cows in India, police said Wednesday, as tensions rose over the slaughter of an animal Hindus consider sacred.

No arrests have yet been made, but police said they had registered a murder case over 55-year-old Pehlu Khan's death in hospital on Monday, two days after a mob attacked his cattle truck on a highway in Alwar in the western state of Rajasthan.

At least six more people were injured when the truck was attacked by around 200 Hindu vigilantes, who police are still trying to identify.

But police also said they were preparing a case against the survivors of the attack, whom they suspect of trying to smuggle the cattle across state borders.

Cows are considered sacred in Hindu-majority India, where squads of vigilantes roam highways inspecting livestock trucks for any trace of the animal.

Slaughtering cows is illegal in many Indian states and some also require a licence for transporting them across state borders.

Alwar police chief Rahul Prakash said the victim and his associates were returning to their home state of Haryana when the mob intercepted their vehicle.

Prakash said the six others have now been discharged from hospital, adding that a postmortem would determine the cause of Khan's death.

"We are yet to receive the postmortem report but he had multiple rib fractures," he told AFP.

Another officer, Ramesh Chand Sinsinwar, told AFP police were preparing a case against the survivors.

"They were carrying eight bovines in the mini truck without permission. We will file a case against the survivors after concluding our investigations," said Sinsinwar, who is heading the investigation in the attack.

Rajasthan home minister Gulab Chand Kataria told reporters that both sides were to blame for the incident.

"It is illegal to transport cows, but people ignore it and cow protectors are trying to stop such people from trafficking them," Kataria told reporters.

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At least 10 Muslim men have been killed in similar incidents across the country by Hindu mobs on suspicion of eating beef or smuggling cows in the last two years.

In 2015 a Muslim man was lynched by his neighbours over rumours that he had slaughtered a cow. Police later said the meat was mutton.

Last month a hotel manager was beaten by a mob and his restaurant sealed in Jaipur after Hindu vigilantes accused him of serving beef.

Critics say the vigilantes have been emboldened by the election in 2014 of Prime Minister Narendra Modi's Hindu nationalist Bharatiya Janata Party.

Last year Modi criticised the cow-protection vigilantes and urged a crackdown against groups using religion as a cover for committing crimes.

But in March he appointed a right-wing Hindu priest to head the country's most populous state Uttar Pradesh, which is also home to much of the country's meat industry.

Shortly after Yogi Adityanath was sworn in, police began shutting butcher shops, grinding much of the industry to a halt.