The majority of "meat dogs" in China are stolen pets and stray dogs, according to an investigation published this month by Hong Kong-based charity Animals Asia, though eating dog is unusual in most parts of China.
Around 30 million households in China are estimated to keep dogs as pets, helping to fuel the growing animal rights movement in China.
This year the dog meat festival has been targeted by British Comedian Ricky Gervais, who posted a series of messages on Twitter with the hashtag "StopYuLin2015".
The city's government has tried to distance itself from the event.
"Some residents of Yulin have the habit of coming together to eat lychees and dog meat during the summer solstice," the city's news office wrote on Sina Weibo, a Chinese Twitter equivalent.
"The 'summer solstice lychee and dog meat festival' is a commercial term, the city has never (officially) organised a 'dog meat festival'," it added.
Eating dog is not illegal in China, but the government called on meat vendors to respect food safety laws.
"Yulin is an open, tolerant and civilised city," it said. "We welcome people across the world to pay attention to Yulin.