The largest traditional animal sacrifice in the world began last weekend in southern Nepal with an estimated 4,000 buffalo, goats, and pigeons slaughtered on Friday alone.

The two-day festival, called Gadhimai Mela Festival, takes place at the Gadhimai temple about 100 miles south of Kathmandu.

The festival is held every five years, during which hundreds of thousands of animals are killed in the name of the Hindu goddess of power. Devotees believe the ritual will bring them good luck.

In 2009, an estimated 350,000 animals were killed. Close to 500,000 animals were expected to be sacrificed this year, despite campaigns to ban the festival.

Sacrificed buffaloes lie on the ground of an enclosed compound during the sacrificial ceremony November 28, 2014. Navesh Chitrakar/Reuters

Millions of Hindus from all over India and Nepal participate in the festival to honor the Goddess Gadhimai, a Hindu deity who devotees believe will grant them wishes if they sacrifice animals and birds. Devotees gather during the ritual before the sacrificial ceremony, November 28, 2014. Navesh Chitrakar/Reuters

The Sword-wielding Hindu devotees began slaughtering the animals on Friday, ignoring calls by animal rights activists to put an end to the world's largest animal sacrifice ritual. Navesh Chitrakar/Reuters

In past years, nearly 70% of the animals entering Nepal to be slaughtered came from India. That figure has dropped since India's Supreme Court banned the illegal entry of animals to Nepal, especially for the Gadhimai Mela. A man sits in a tractor to load the sacrificed buffalos a day after the sacrificial ceremony, November 29, 2014. Navesh Chitrakar/Reuters

The festival is partially funded by the government of Nepal as the fair brings in tourists and money. Temple authorities also charge entry and parking fees. A street vendor makes sweets along the street to sell them to devotees, November 29, 2014. Navesh Chitrakar/Reuters

Animals are coralled into holding pens in a large field before having their throats slit or their heads chopped off.

A sick buffalo calf lies in an enclosure on the eve of the sacrificial ceremony November 27, 2014. Reuters

"It is very festive here, everyone is excited," Mangal Chaudhary, the head priest at the slaughter site near a temple devoted to Gadhimai, told AlJazeera. A family poses for a picture in front of the carcasses of sacrificed buffalos, November 29, 2014. Navesh Chitrakar/Reuters

After the buffalo are killed, their heads are thrown into a freshly dug large pit in the field, and their hides are sold to the highest-bidding contractors. A man removes the tongue from the head of a sacrificed buffalo the day after the sacrificial ceremony, November 29, 2014. Navesh Chitrakar/Reuters

Activists have petitioned Nepal's president to end this "cruel tradition" that began about 260 years ago. Still, the animal sacrifice ritual draws over 2 million Hindus to the festival site and remains an important religious holiday.