Teresa Zhan, a pharmacist in Manhattan's Chinatown, had not seen protective face masks sell out in her 10 years as an employee until this week, when China's coronavirus arrived in the United States just days before Lunar New Year celebrations.

More than a dozen pharmacies in the tiny district had run out of face masks or only had a few left on Friday. Pharmacists said hundreds of locals had rushed to buy masks for protection from the newly discovered coronavirus that has killed 26 people in China and infected at least 800 others, including a case in Chicago and another near Seattle.

More:

"Everybody's been coming in the morning and saying, do you have face masks? Do you have face masks?" Zhan said.

During a typical flu season, customers will buy one or two surgical masks at a time to protect themselves from the virus, Zhan said.

"Now, they're like, give me the whole box," she said.

The bulk purchases of masks, as many as 250 at a time, started earlier this week as people prepared to travel to China for Saturday's Lunar New Year holiday, which health officials fear could accelerate the infection rate. Many people also hope to send masks to their families in China.

"Some people buy it to send it home, because right now in China, they are out of all the masks," said Ryan Ngo, a technician at Tu Quynh Pharmacy, which sold its last box of masks on Thursday.

The World Health Organization on Thursday declared the virus an "emergency in China", but said it was too soon to call it a global health emergency.

Symptoms include fever, difficulty breathing and coughing.

Annie Chan, a 30-year-old accountant, was searching for face masks on Friday for her cousin, who was travelling to New York from Hong Kong for the holiday. Chan checked Harmony Pharmacy, which had run out of protective surgical masks but still had a few boxes of a less protective brand.

"I honestly don't know what she wants, I was just trying to see what places still have them," Chan said.

The US Centers for Disease Control and Prevention (CDC) has confirmed two US cases of the coronavirus, in the states of Illinois and Washington, and said on Friday as many as 63 potential cases were being investigated.

People in Chinatown were also flocking to herbal shops to stock up on home remedies. Their sense of alarm reminded herbal shop manager Patrick Siu of the 2003 outbreak of severe acute respiratory syndrome (SARS), which originated in China and killed 774 people worldwide.

For the first time since the SARS outbreak, Siu noticed nearly twice as much demand this week for the Isatis root, used in Chinese traditional medicine to treat respiratory illness. Customers have called ahead to ask Siu to place some on hold.

Given that health officials do not yet know how dangerous the coronavirus is and how easily it spreads, their caution is justified, Siu said.

"You never know what will happen," he said. "If you are the one, then maybe your whole family is the victim."