The world's biggest animal sacrifice began in Nepal today with the killing of the first of more than 250,000 animals as part of a Hindu festival in the village of Bariyapur, near the border with India.

The event, which happens every five years, began with the decapitation of thousands of buffalo, killed in honour of Gadhimai, a Hindu goddess of power.

With up to a million worshippers on the roads near the festival grounds, this year's fair seems more popular than ever, despite vocal protests from animals rights groups who have called for it to be banned. "It is the traditional way, " explained 45-year old Manoj Shah, a Nepali driver who has been attending the event since he was six, "If we want anything, and we come here with an offering to the goddess, within five years all our dreams will be fulfilled." .

Crowds thronged the roads and camped out in the open, wrapped in blankets against the cool mist. The festivities included a ferris wheel, fortune-telling robots and stalls broadcasting music and offering tea and sugary snacks.

As dawn broke, the fair officially opened with the sacrifice of two rats, two pigeons, a pig, a lamb and a rooster in the main temple, to cheers of "Long live Gadhimai" from spectators pushing against each other for a better view.

In the main event, 250 appointed residents with traditional kukri knives began their task of decapitating more than 10,000 buffalo in a dusty enclosure guarded by high walls and armed police.

Frightened calves galloped around in vain as the men, wearing red bandanas and armbands, pursued them and chopped off their heads. Banned from entering the animal pen, hundreds of visitors scrambled up the three-metre walls to catch a glimpse of the carnage.

The dead beasts will be sold to companies who will profit from the sale of the meat, bones and hide. Organisers will funnel the proceeds into development of the area, including the temple upkeep.

On the eve of the event, protesters made a final plea to organisers by cracking open coconuts in a nearby temple as a symbolic sacrifice. "It is cruel and inhumane. We've always been a superstitious country, but I don't think sacrifice has to be part of the Hindu religion," said the protest organiser, Pramada Shah.

The campaign has the support of the French actor Brigitte Bardot, who has petitioned the Nepalese prime minister, Madhav Kumar Nepal, about the issue. But the government, which donated £36,500 to the event, has shown no sign of discontinuing the centuries-old tradition. An attempt by the previous government to cut the budget for animal sacrifice provoked street protests.

Chandan Dev Chaudhary, a Hindu priest, said he was pleased with the festival's high turnout and insisted tradition had to be kept. "The goddess needs blood," he said. "Then that person can make his wishes come true."