Up to one million Hindu devotees have gathered in a village in Nepal to witness the slaughter of hundreds of thousands of animals in a mass sacrifice that has drawn widespread criticism.

Worshippers travelled long distances, many coming from neighbouring India, to attend the two-day Gadhimai festival, which honours the Hindu goddess of power and takes place once every five years in southern Nepal.

A huge cry of "Long Live Gadhimai!" went up after the village temple's head priest launched the event with the ritual sacrifice of two rats, two pigeons, a rooster, a lamb and a pig.

The crowd then rushed to a nearby field where 250 sword-wielding butchers began the mass slaughter of around 20,000 buffalo, brought by devotees to be sacrificed near the holy temple.

"This is a very special day for Hindu devotees," head priest Mangal Chaudhary Tharu said as the festival began.

"All the people who came here to worship Gadhimai have been waiting a long time for this day. I am very proud to be part of this event," added Mr Tharu, the fourth generation of his family to serve as a priest at the temple.

A reporter at the scene said up to a million devotees were crammed into the area for the festival. Many were from India, where some states have banned animal slaughter for religious purposes.

Chanchal Shah, a 55-year-old farmer from the northern Indian state of Bihar, travelled to Bariyapur by tractor with dozens of relatives to sacrifice a buffalo in thanks for the birth of his grandson.

"We have come to celebrate the birth of my daughter's son," Mr Shah said.

"She got married two years ago and I had promised I would sacrifice an animal after she had her first child. I know that sacrificing is a bad idea, but I am scared the goddess will be angry if I do not keep my promise."

'Cruel' sacrifice

Animal rights activists, who have waged a vocal campaign to have the festival stopped, say they believe their message that sacrifice is cruel is beginning to be heard in deeply conservative, majority-Hindu Nepal.

Their cause is supported by the well-known Indian animal rights activist Maneka Gandhi and by the French film star turned campaigner Brigitte Bardot, who this month wrote to Nepal's president urging him to ban the practice.

But the government has refused to put a stop to what it says is a centuries-old religious tradition.

Mahesh Yadav, a Nepalese farmer who arrived with a black goat tethered to the back of his bicycle, said he wanted to thank Gadhimai for giving him a son.

"I had seven daughters in a row so I promised the goddess I would sacrifice a goat if she gave me a son," he said.

"Eight years ago the goddess listened and my son was born."

The buffalo slaughter took place in a field surrounded by a three-metre wall, and will be followed by the ritual sacrifice of around 300,000 goats, sheep and birds.

Many festival-goers scaled the wall to get a better view of the killings, carried out by volunteers.

Armed police were deployed around the temple grounds, but the event passed off mainly peacefully.

- AFP