Kathmandu, Nepal (CNN) -- The two-day ritual slaughter of tens of thousands of animals -- among the world's largest sacrifice of animals -- began Tuesday in southern Nepal, officials said.
About 200,000 animals, including male water buffalo, goats and roosters will be slaughtered, despite protests from animal rights activists, according to the chief priest of the festival.
"This is a divine power center," Mangal Chaudhary, the head priest of the Gadhimai temple, said by phone. "When people wish for a son, a job, good health or anything else come true, they make an offering to the Gadhimai goddess."
He expects more than 5 million people -- 60 percent from India, which shares an open border with Nepal -- to attend the festival.
About 15,000 male water buffalo will be slaughtered, up from 12,000 five years ago, said Chaudhary, who is the 10th generation of his family to serve as chief priest.
Water buffalo are slaughtered on the first day, and other animals on the second day.
Government officials say they cannot stop the centuries-old tradition, despite opposition from animal-rights activists from Nepal and India.
"This is a matter of people's religion and belief," said chief district officer Tara Nath Gautam, the highest-ranking government official in Bara.
Animal rights activists say they aren't looking for a sea change.
"We do not expect this practice to stop overnight. A sustained effort is needed so that, sometime, the practice will end," said Nepali animal rights activist Pramada Shah.
Though meat from the sacrificed animals is given to devotees, the hides of water buffalo are taken by the festival management committee to sell. The heads are buried on the temple premises, which spread over three square kilometers, Chaudhary said.
Buffalo is eaten by low castes in Nepal and India, but goat meat is eaten by a wider population.
An estimated 100,000 to 200,000 goats are sacrificed, Chaudhary said.
Journalist Manesh Shrestha contributed to this report.