Millions of Hindus gathered in southern Nepal today, to take part in the Gadhimai festival – thought to be the world’s largest animal sacrifice ritual.

Devotees believe the event brings good luck, and will encourage Gadhimai, the Hindu goddess of power, to answer their wishes.

The ritual begins before dawn in the fields outside Gadhimai temple in Bariyarpur, where a priest trickles his own blood combined with that of a rat, chicken, pigeon, goat, and pig.

Thousands of vehicles packed with families carrying goats and birds intended for sacrifice travelled along the road leading to the temple today.

To end the first day of the event, thousands of buffaloes enclosed in a compound surrounded by a high wall, are decapitated by a group of specially chosen men using curved kukri knives.

On the first half of the two day event held in the jungles of Bara district, around 160 miles (100 miles) south of Katmandu, some 5,000 buffaloes were killed – and many are yet to be slaughtered.

During the 2009 festival, an estimated 200,000 animals and birds were sacrificed.

Animal sacrifice at the Gadhimai festival in Nepal Show all 16 1 /16 Animal sacrifice at the Gadhimai festival in Nepal Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A group of devotees elevate as a blessing their traditional kukri knifes before the beginning of the animal sacrifices during the celebration of the Gadhimai festival in Bariyarpur, Nepal. Omar Havana/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A member of the police forces controls the crowd gathered for animal sacrifices. Omar Havana/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A water buffalo walks between slaughtered animals. The Hindu festival lasts one month and takes place every five years. EPA/LAXMI PRASAD NGAKHUSI PICK UP Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival Hindu priests stand over blood from a goat and a chicken after the animals were sacrificed during the Gadhimai festival on November 28, 2014. AFP/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival Devotees climb a tree to observe the sacrificial ceremony of the "Gadhimai Mela" festival held in Bariyapur November 28, 2014. Reuters Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival Devotees walk toward the main entrance of the sacrifice area carrying a water buffalo during the celebration of the Gadhimai festival on November 28, 2014 in Bariyarpur, Nepal. Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival Butcher prepares to slaughter a buffalo inside an enclosed compound. REUTERS/Navesh Chitrakar Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A butcher holds his blade high as he looks for a buffalo to be sacrificed. REUTERS/Navesh Chitrakar Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A buffalo about to be sacrificed sits inside an enclosed compound. REUTERS/Navesh Chitrakar Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A butcher walks with a bloodied blade as he looks for an animal to kill. AFP PHOTO/ROBERTO SCHMIDTROBERTO SCHMIDT/AFP/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival Hindu devotees walk on a country road leading to the village of Bariyarpur to celebrate the Gadhimai festival on November 27, 2014. AFP/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A butcher holds up his sword as he attends the mass ritual before slaughtering water buffalo. EPA/LAXMI PRASAD NGAKHUSI Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A devotee offers a pigeon to the Goddess during the celebration. Omar Havana/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A boy and girl smile as they play with their windwheels in a country road leading away from the village of Barayarpur after they and their families participated in the Gadhimai festival on November 28, 2014. AFP/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A devotee prays during the celebration of the Gadhimai Festival in Bariyarpur, Nepal. Omar Havana/Getty Images Animal sacrifice at the Gadhimai festival in Nepal The Gadhimai festival A family walks amid the dust of a country road after dark as they leave the village of Baryarpur after attending celebrations of the Gadhimai festival. Millions of Hindu devotees from Nepal and India migrate to the village to honour their goddess of power. The celebrations includes the slaughtering of hundreds of thousands of animals, mostly buffalo and goats. Worshippers have spent days sleeping out in the open and offering prayers to the goddess at a temple decked with flowers in preparation. SCHMIDT/AFP/Getty Images

Most people who attend the festival are from neighbouring India, even though that country bans the export of animals for the festival. The measure, put into place after the 2009 festival, has halved the number of animals to be slaughtered this year.

While organisers and the authorities defend the festival held every five years as a generations-old tradition, animal rights activists decry it as barbaric.

One festival-goer, Rajesh Shah, told the Guardian that he promised Gadhimai he would sacrifice a goat in her honour if his business was successful, as he cooked the animal he had just killed. He added he kept his promise to Gadhimai despite hearing complaints about the event.

Shristi Singh Shrestha, an animal rights activist with Animal Welfare Network Nepal, told the newspaper she felt “sad” and “defeated” because the group was unable to stop the slaughter.