Hairy crabs, one of the most popular delicacies of the season in eastern China, are being sold in a vending machine at an office building in downtown Shanghai.

As news spread, eager customers hurried on Thursday, only to find that the machine, which holds 100 crabs, had run empty by noon.

The hairy crabs came from Yangcheng Lake, a freshwater lake in Suzhou, Jiangsu province, that enjoys a reputation as the home of the best crabs, which typically weigh between 100 and 150 grams and sell for 15 yuan ($2.25) each - considered a bargain, as such crabs usually fetch at least 10 yuan more at regular markets, according to an employee who was tending the machine and asked not to be named.

Price, however, explains only part of the machine's popularity.

Qiu Yan, who works nearby, approached the vending machine during her lunch break, thinking it would be an interesting and convenient shopping experience. "I really want to try this, but it's empty," she lamented.

The machine, located at the headquarters of Yiguo Fresh Food, an e-commerce platform that sells fresh food in Changning district, is a pilot program launched by Yiguo and Tmall.

The customer service department at Tmall said the companies are using the machine to test the market. They might place more machines across the city based on the three-day trial of the machine.

Hairy crabs have long been considered an autumn delicacy in China, especially among residents of the Yangtze River Delta.

High demand for the seasonal dish there has made sales of hairy crabs, especially those harvested from Yangcheng Lake, a focus of competition among fresh food retailers, which are now dominated by e-commerce giants.

As the e-commerce giants compete for market share, they face a major challenge: how to deliver hairy crabs fresh to customers at a reasonable cost.

Since 2008, insiders have considered automatic vending machines - which can be placed anywhere across the city and require minimum management - as one of the most promising retail solutions for the crabs.

Nanjing, Jiangsu province, reported the first hairy crab vending machine in a subway station in 2010. Other cities, including Suzhou and Hangzhou, Zhejiang province, also introduced machines for the delicacy, but the number of machines is limited.

Ensuring quality and service also remains a challenge. While the vending machines can easily maintain a temperature between 3 and 6 C to keep the crabs in a dormant state, the stock inside the machine needs to be replaced every 48 hours.

To maintain quality, Yiguo printed its customer service phone number on the machine, with a message saying that if any quality problem is noticed, a customer can take a photo and call the service line within eight hours. But the high demand for the crabs could render that concern moot.

Yuan Weining, a customer who wanted to buy from a vending machine, said that freshness is a key consideration, but residents also want authentic Yangcheng Lake hairy crabs.

"Hairy crabs from Yangcheng Lake always deserve a buy," he said.

He Qi in Shanghai contributed to this story.