Tightly crushed together in an area about the size of a football field fenced with barbed wire, more than 2,000 buffalo stand waiting for their death. Deprived of adequate water and food, they snort and snuffle in pain.

The animals are just some of the thousands prepared for sacrifice as part of this year’s Gadhimai festival in Nepal, which takes place once every five years and holds the dubious honour of being known as the world’s bloodiest festival.

For more than two centuries, the festival has drawn millions of Hindu devotees to the Gadhimai temple of Bariyarpur in early December, out of the belief that animal sacrifices to the Hindu goddess Gadhimai will end evil and bring prosperity.

Devotees raise their sacrificial blades – known as khukuris – as the festival begins. Photograph: Navesh Chitrakar/Reuters

According to legend, the first sacrifices in Bariyarpur were conducted several centuries ago when the goddess Gadhimai appeared to a prisoner in a dream and told him to offer blood and establish her temple. When he awoke, his shackles had fallen open and he was able to leave the prison and build the temple, where he sacrificed animals to give thanks.

However, in recent years, it has also become one of the most polarising traditions in Nepal, dividing those who see it as a touchstone traditional Hindu ceremony and those who believe it is an outdated monument to animal cruelty. In 2009, it is estimated around a quarter of a million animals were slaughtered. The figure for 2014 was about 200,000.

This year’s event is the first since a supreme court ruling in 2015 that directed the government to discourage bloodshed, but thousands of creatures are still set to be killed over the two days.

Even if they could not prevent the slaughter, activists were tending to the animals in their final hours in an attempt to minimise suffering.

Her hands and face smeared with blood and mud, Sneha Shrestha, president of the Federation of Animal Welfare Nepal, spent Monday treating wounded buffalo calves with saline water and medicine, checking their temperatures and trying to bring them food and water.

“We are not against traditions and culture but if such practices hurt animals then we must step forward to end them,” said Shrestha.

At the crack of dawn on Tuesday morning the festival began with the Pancha Bali, the sacrifices of a rat, a goat, a rooster, a pig and a pigeon. By 9am, about 200 butchers began to take their khukuris – a type of Nepalese blade – to the necks of the buffaloes. The air was filled with the cries of the animals. By the end of the day, between 3,000 to 6,500 buffalo had been beheaded.

Hindu devotees perform a ritual at a temple near the sacrifice enclosure. Photograph: Prakash Mathema/AFP/Getty

Worshippers who came to the temple defended the festival’s traditions. “Those who are against the festival will continue to protest and those who wish to worship the goddess will do so,” said a woman from Kolhabi. “No one can stop it.Our faith is important and sacrifices validate it.”

“Look at these hundreds of people,” she added, pointing to a sea of attendees. “They are here because of their faith.”

Some of those who have voiced opposition to Gadhimai have faced severe backlash and even threats of violence. Manoj Gautam, an animal rights activist who has been campaigning against the festival for 11 years, was attacked a few months ago. He said he felt “saddened and enraged”.

Gautam accused local and state institutions of “forsaking their duty by hiding behind an institutional veil”.

On Monday, Gautam filed a contempt case in Kathmandu’s supreme court against the Nepalese government and Gadhimai temple committee for disregarding the 2015 supreme court ruling.

Bara’s chief district officer, Phanindra Mani Pokharel, said that ending the mass slaughter of animals was not simple, as it was likely to lead to social unrest. He also pointed to the economic significance of the festival to Chamar’s community.

Motilal Kushwaha, general secretary of Gadhimai Mela Organizing Committee, said: “We have done our best to make this festival a good one in terms of security, health and water sanitation. Also, we are on the side of discouraging sacrifices according to the 2015 supreme court verdict.

“There’s no definite answer as to when this festival will end but it will one day.”