The slaughter of more than 5,000 buffaloes at the Gadhimai Hindu festival in Nepal has drawn global condemnation from animal charities.

Many more buffaloes and farm animals including chickens, goats and pigs are due to be killed as part of what is 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.

Several charities had worked to stop the slaughter – the first of its kind since an estimated 200,000 animals and birds were sacrificed in 2009 – but only succeeded in pressuring the Indian Government into stopping animals being transported across the border.

Joanna Lumley is among the celebrities opposing the festival and led a protest in London last month with the charity Compassion in World Farming.

At a rally outside the Nepalese embassy, she said: “I love Nepal – both the land and its people. The Gadhimai animal sacrifice festival entails horrendous animal suffering and is a complete anomaly in this wonderful country.”

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 on Friday.

To end the first day of the event, thousands of buffaloes were decapitated by a group of specially chosen men using curved kukri knives.

“The sights and sounds are unimaginable,” wrote Jayasimha Nuggehalli director of the Indian branch of the Humane Society International. “Pools of blood, animals bellowing in pain and panic, wide-eyed children looking on, devotees covered in animal blood, and some people even drinking blood from the headless but still warm carcasses.”

Shristi Singh Shrestha, an animal rights activist with Animal Welfare Network Nepal, told the Guardian she felt “defeated” because the group was unable to stop the slaughter but the number of killed livestock was falling.

“However, the positive thing is that the number of animals killed has come down…we hope there will be no killing of any animal at the next festival,” she said.

An Italian charity, Partito EcoAnimalista, called Gadhimai “unparalleled religious madness”, saying the buffaloes are not given food or water for several days before the slaughter to make them docile and weak.

Peta also launched a petition calling for the “horrifying display of violence” to be stopped.

Its letter read: “The frenzied slaughter of hundreds of thousands of goats, chickens, buffalo and other animals only tarnishes Nepal's international reputation. Numerous animals, already weakened by their long journeys, die from exhaustion, starvation or dehydration before the massacre begins.”

Several Hindu leaders have also argued that the ritual goes against core religious beliefs.

Surya Upadhya, chairman of the Nepalese Hindu Forum in the UK, said: “The Nepalese Hindu Forum in the UK completely opposes animal sacrifice as Hinduism does not sanction the killing of living beings.

“There should not be any place for this inhumane, barbaric sacrifice of innocent animals in the name of any religion”.

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

The interim law banning the transport of animals from India had led to almost 2,500 being confiscated and 114 arrests in Bihar, West Bengal, Uttarakhand, Uttar Pradesh and Sashastra Seema Bal, said N.G. Jayasimha, the managing director of Humane Society International India.

Pictures of the slaughter showed carcasses of countless beheaded and mutilated animals surrounded by pools of blood as young boys watched the bloodshed.

The gruesome images provoked outrage on Twitter, with global calls for Gadhimai to be stopped before the next ritual is due in 2019, although some defended the tradition.