As many as 15,000 dogs are tortured, killed and cooked to be sold at Yulin Lychee and Dog Meat Festival every year.
Canine meat is considered a delicacy in China, where about £10m worth of dogs and £4m cats are sold for their meat annually.
But 1.5 million people have now signed a petition calling for an end to the cruel festival.
Claire Bass, UK director of Humane Society International (HSI), said: “Yulin is one relatively small example of a much larger, uglier issue that thousands of dedicated Chinese activists are working to stop.
“Contrary to the assumptions by many in the West, most people in China don’t eat dogs and in fact they are horrified at the thought of a trade that takes their canine companions away from them.”
Sending her support for the petition, actress Dame Judi Dench said: “It fills me with sadness to think that the Yulin dog meat festival is just around the corner again.
“So I wanted to send this message as a symbol of my solidarity with all the thousands of people in China against the dog meat trade, who love their dogs and cats just as much as we do, but who go through the awful heart ache of having them stolen by dog thieves.”
Most dogs and cats caught up in China’s meat trade are believed to be strays snatched from the streets and stolen pets, according to HSI.
Dogs and cats are typically bludgeoned to death in front of each other, put into a de-hairing machine to remove fur, and then blow-torched for sale to markets, the organisation said.
The animals are also still sometimes slaughtered in public places.
Thousands descend on the festival on 21 June each summer to celebrate the summer solstice – the longest day of the year.
According to folklore, eating the meat during the summer months brings luck and good health.
Some also believe dog meat can ward off diseases and heighten men’s sexual performance.
Cat meat, fresh lychees and liquor are also available at the 10-day event.
Just five days before this year’s festival, Chinese animal activists managed to rescue 62 dogs from a Yulin slaughterhouse.
Many of them are now being cared for by HSI at a shelter in northern China.