A fresh campaign calling for an end to the annual Yulin dog meat festival in China has been launched by animal rights campaigners.

It comes as distressing new images from the region show slaughtered dogs and cats piled high as preparation begins for the event in June, described by one expert as "a scene from a nightmare".

Warning: This article contains details and images which some people may find upsetting.

More than four million people from around the world signed an online petition calling for an end to the tradition last year - and the Humane Society International (HSI) said it is hoping this year's #StopYulin drive will attract even more attention.

A number of animal charities in China - including the Capital Animal Welfare Association, VShine Animal Protection, The Ta Foundation, Hong Kong SPCA and China Animal Protection Power - have now joined the protests.

The HSI's China policy specialist, Dr Peter Li, visited some of the slaughterhouses earlier this month and took pictures and video footage of what he found.

Slaughtered dogs and cats for sale in Yulin Credit: Humane Society International

Cats and kittens crammed into a cage in one of the slaughterhouses Credit: Humane Society International

Dogs and cats were seen crammed into tiny, filthy cages - many of them wearing collars, indicating they were family pets who had been stolen.

He said he witnessed the animals being bludgeoned to death with metal rods, in full view of their cage-mates, before being disembowelled and dismembered.

The blood was left to seep into the surrounding holding pens, he said - while some of the slaughterhouses were situated within earshot of schools teaching children as young as six.

The HSI estimates that around 300 dogs a day are slaughted in Yulin - with thousands more expected to die during the annual meat festival.

An estimated 300 dogs a day are killed for meat in Yulin Credit: Humane Society International

Speaking after his trip, Dr Li said it had been "one of the most harrowing" visits he had been on.

The dogs and cats I saw were visibly traumatised, their spirits broken from their terrifying ordeal. It’s hard to imagine their mental suffering, watching other dogs being killed, disembowelled and dismembered in front of them. Dr Peter Li, HSI

Blood is left to seep into the holding cages Credit: Humane Society International

Dogs are beaten and killed in front of their cage-mates - and sometimes within earshot of nearby schools Credit: Humane Society International

Between 10 and 20 million dogs are killed for food every year in China, with many traders violating the law by stealing the animals for meat and animal welfare guidelines, as well as breaching food safety rules by keeping them in unhygienic conditions.

The HSI said the World Health Organisations has confirmed the trade is linked to both cholera and rabies.

Comedian and animal rights campaigner Ricky Gervais has once again joined forces with the HSI, calling for an end to the festival and promoting their online petition.

The HSI hopes to present its petition to Chinese officials before the Yulin dog meat festival begins on June 21.