Hindu worshippers have begun beheading thousands of buffalo in Nepal as part of what is thought to be the world’s largest animal sacrifice event.

The Gadhimai festival started in the early hours of Tuesday morning as a priest killed a goat, rat, chicken, pig and pigeon and then offered blood from his own body.

Around 200 butchers wielding curved kukri knives then descended on a walled temple arena containing an estimated 3,500 buffalo to behead the animals.

Campaigners for animal rights charity Humane Society International described seeing baby buffaloes bellowing as they watched their mothers being decapitated.

They said others collapsed from exhaustion, sickness and stress as worshippers attempted to drag them to their deaths.

Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Show all 20 1 /20 Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ A Hindu devotee slaughters a buffalo as an offering to Hindu goddess Gadhimai. AFP via Getty Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI India plead with Gadhimai Temple priest Mangal Chowdhury to stop the killing Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ It is thought to be the world's biggest animal sacrifice which takes place in a remote area of Nepal Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Buffaloes are kept inside an enclosure awaiting sacrifice Reuters Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Devotees raise their sacrificial blades Reuters Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Hindu devotees watch behind a barb-wired wall AFP via Getty Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ A butcher gets ready to sacrifice animals AP Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Gadhimai sacrifice in Nepal Arkaprava Bhar/Humane Society International India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI/India at the India-Nepal border assist the law enforcement with inspecting vehicles and seizing animals illegally transported across the border for sacrifice at Gadhimai Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Gadhimai Festival Nepal December 2019 Arkaprava Bhar Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ A butcher swings his blade to sacrifice a buffalo Reuters Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI/India at the India-Nepal border assist the law enforcement with inspecting vehicles and seizing animals illegally transported across the border for sacrifice at Gadhimai. Arkaprava Bhar Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Hindu devotees hold a duck and chicken ahead of the start of sacrificial offerings AFP via Getty Images Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ A Hindu devotee watches rituals ahead of the start of sacrificial offerings AFP via Getty Images Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI/India at the India-Nepal border assist the law enforcement with inspecting vehicles and seizing animals illegally transported across the border for sacrifice at Gadhimai Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ A Hindu devotee bringing a goat for sacrifice AFP via Getty Images Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Hindu devotees holding knives look on as religious mantras are sung AFP via Getty Images Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI/India at the India-Nepal border assist the law enforcement with inspecting vehicles and seizing animals illegally transported across the border for sacrifice at Gadhimai. Arkaprava Bhar Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ Gadhimai sacrifice in Nepal December 2019 Arkaprava Bhar Arkaprava Bhar/HSI India Gadhimai Hindu festival: World’s ‘largest animal sacrifice’ HSI India assists the law enforcement at Indo-Nepal border in checking vehicles and seizing animals illegally transported across the border ahead of the Gadhimai animal sacrifice festival in Nepal. HSI/India is working with partners FAWN and PFA as part of the #BloodlessGadhimai initiative. ArkaPrava Bhar Arkaprava Bhar/HSI India

Thousands of people from Nepal and neighbouring India travelled to Bariyarpur village to witness the festival, which occurs every five years.

A Hindu devotee prepares to slaughter a buffalo (AFP via Getty Images)

The sacrifices went ahead despite temple authorities announcing a ban in 2015 and Nepal’s supreme court directing the government to reduce animal sacrifice a year later.

Alokparna Sengupta, managing director of Humane Society International in India, said being at the festival was “one of the most depressing and challenging experiences of my life”.

“The suffering of these animals is so upsetting, they have endured exhausting journeys to get here and are paraded in front of a baying crowd as all around them they witness other animals being decapitated one by one,” she said.

Devotees raise their sacrificial blades at the sacrificial ceremony (REUTERS)

“Buffalo calves look on in bewilderment as their mothers are slaughtered in front of them. The hysteria and apparent jubilation at seeing confused and frightened animals being slaughtered was very disturbing.”

In the last week the Indian border force and campaigners seized hundreds of baby goats, pigeons and buffaloes at the border.

“We may not have a bloodless Gadhimai this time, but we are determined that one day we will see an end to this gruesome spectacle,” Ms Sengupta added.

Mimi Bekhechi, Peta’s director of international programmes, said: “Nepali officials promised – but have failed – to protect thousands of petrified animals from being dragged and transported to a violent mass killing that starts today.

“The government must act forcefully to prevent this bloodbath from taking place again or feel the impact of a tourist boycott.”

She added: “Devotees are bringing universal condemnation to a wonderful religion – which needn’t be based on fear and cruelty – and just as widow-burning and human-baby sacrifice have ended, so must the horror of an animal-slaughter festival.

“Gruesome images of animals looking up pitifully and struggling as they’re hacked into pieces ruin Nepal’s reputation, and we urge all of its compassionate citizens to join the international clamour for an end to such barbarity.”

In 2009, at the height of the festival, around 500,000 buffaloes, goats, pigeons and other animals were killed. After protests in the intervening years 30,000 were killed in 2014.