The most sought-after commodity in areas hit by the H7N9 flu outbreak is a 10-yuan ($1.60) herbal remedy, indigowoad roots, or banlangen, which has been selling out in stores across Shanghai and Jiangsu, Zhejiang and Anhui provinces.
Daily supplies at pharmacies are being cleared within hours, and demand is so high the government has imposed strict price restrictions to prevent profiteering.
No one is absolutely certain what the humble herb can do to fight the disease, but Jiangsu provincial health bureau said on April 3 that banlangen can keep the H7N9 virus at bay, something which has eluded most advanced medicines, suggested pharmacists.
"No one knows what might happen with bird flu, so they are buying it," said a clerk at the Renshoutang Pharmacy in Shanghai.
Xiong Wei, the general manager of LBX Pharmacy in Shanghai, said sales of the herb surged between Thursday and Sunday.
"Demand soared from April 3. We had to order 4,800 packets of banlangen the next day from Hangzhou because some stores in Shanghai reported a shortage.
"By Saturday, almost every city in the Yangtze River Delta had reported a shortage and we have had to order the drug from other parts of the country."
On usual days, Xiong said LBX sells about 300 packets of banlangen a day. Ever since the bird flu outbreak, sales have been about 10 times that.
More than 3,000 packets were sold on Sunday, Xiong added, although sales had calmed in recent days.
"But we have promised not to raise prices at any of our stores, and hope other drugstores don't either."
An employee surnamed Yang at the pharmacy of Shanghai Shuguang Hospital, which is affiliated to Shanghai University of Traditional Chinese Medicine, said: "Banlangen at our hospital is priced at 5.4 yuan a pack.
"So far sales have been steady, with no significant growth."
Price control officials in Nanjing, Jiangsu province, released a notice on Monday urging that prices of all traditional Chinese medicines sold at drugstores and hospitals should not be allowed to increase during the prevention and control period of bird flu.
Xue Li, a sales representative at Nepstar drugstore in South Huaxia Road in Wuxi, Jiangsu province, said it had been selling banlangen in nine- and 10-yuan packs, ever since the news of the outbreak was reported at the beginning of this month.
"For the cheaper ones, fewer than 10 packets are left at the end of every day."
Hua Liping, the manager of a drugstore near Wuxi People's Hospital, said they have been running out of banlangen since Saturday, and was not sure whether they could have the drug restocked until Tuesday.
There are seven major producers of banlangen drugs in China, with Hutchison Whampoa Guangzhou Baiyunshan Chinese Medicine Co the largest, with about 60 percent of the market.
Last year the company's banlangen sales were worth 336 million yuan.