And it is still the favorite of local diners, although new styles of hotpot, such as beef and mild duck soup, have gained in popularity in recent years.

Although there is no hard evidence on how it originated, many believe that Chongqing hotpot emerged from the porters' cuisine of the late 19th century.

Chongqing is a port city surrounded by the Yangtze and Jialing rivers. In the late 19th century, animals from Sichuan, Guizhou and Yunnan provinces were shipped by water. Good meat was shipped and sold to the upper and middle classes.

The internal organs, including stomach and kidney, were discarded or sold cheaply. Porters picked up or bought the organs and cooked them in a boiling pot with spicy sauce.

During World War II, when Chongqing was the wartime capital, the food gained popularity among people from all around the world.

"Hotpot is our city's signature cuisine with a long history," said Li Dejian, head of the Chongqing Hotpot Association.

To maintain its popularity, "the whole industry needs to upgrade its management and cultivate its culture", he added.

The Hotpot Red Book says that in 2013-14, the Chongqing hotpot industry underwent rapid growth thanks to the chain-store business model and overseas expansion.

In 1995, Little Swan became the first Chongqing hotpot restaurant to open a branch overseas when it set up a hotpot eatery in Seattle.

Now from New York to Dubai, the chain stores of famous local Chongqing hotpot places are all over the world.

Last year, the city exported 400 metric tons of packed hotpot soup base to 10 countries and regions, including the United States, Australia and Southeast Asia.