By Joanna Jolly BBC News, Bariyapur

Hundreds of thousands of Hindu devotees have converged on a town in Nepal for a festival which is considered the world's largest animal sacrifice.

The Gadhimai festival, which happens once every five years, is taking place in Bariyapur in southern Nepal.

More than a quarter of a million animals are expected to be slaughtered for Gadhimai - a goddess of power.

Sacrifice is a seen as a way of thanking the deity for good luck, or asking her for fortune and prosperity.

"The goddess needs blood," says Chandan Dev Chaudhury, a priest at the Gadhimai Temple in the centre of the festival site.

"If anyone has a problem, then I will cut the throat of an animal in the temple and that person's problem will be solved."

'Ancient belief'

Many of the worshippers have come from neighbouring India for the two-day festival.

Sixty-year-old Suresh Patak and his family travelled for a day to reach the festival from the Indian state of Bihar.

They have brought a goat to offer to the goddess.

"I have come here to worship Gadhimai. We are dedicated to her," he says.

Devotees have arrived from neighbouring India

"It is our ancient belief."

Festival organisers estimate more than half a million people are already at the festival site.

Many of them, like Suresh, have brought their own animals to be killed.

Behind high brick walls, thousands of buffalo move silently through the winter fog.

They are the largest animals to be sacrificed, but goats, chickens, pigeons and rats will also be killed.

Police inspector Bikesh Adhikari is one of the officials guarding the buffalo enclosure.

"First of all five buffalo are taken and sacrificed at the temple," he says.

"The rest are sacrificed here."

Two hundred and fifty local men have been given licences to slaughter the animals using traditional khukuri knives.

Spectators queue to watch the killing, each paying 20 Nepali rupees (26 cents).

But the scale and method of this sacrifice has angered some Nepalis.

'Cruel and barbaric'

Outside the temple grounds, a small but vocal group of animal rights activists cracked coconuts in a symbolic temple sacrifice.

It was a last minute plea to the organisers of the festival to call off the event.

They say that it is cruel and barbaric and that Hindu gods can be appeased by fruit and flower sacrifices.

"We're just giving out a message, that's all we can do at this stage," says protest organiser Pramada Shah.

The animal sacrifice has angered a lot of activists

"We're not saying stop the Gadhimai Festival - everybody's having a nice time," she says.

"But let's have it in a less gory manner is all we're trying to say."

But it is unlikely the animal sacrifice will stop.

Not only does the Gadhimai festival attract hundreds of thousands of worshippers, it is also big business.

The meat, bones and hides of the animals are sold to companies in India and Nepal.

Local hotels and restaurant owners thrive during the festival period.

And while protestors say they hope to raise awareness about the issue of animal cruelty, this ancient and bloody homage to the goddess Gadhimai looks set to continue.