According to the BBC, the masks began selling out in Seattle, where the first case of coronavirus was reported in the U.S. The outlet said other cities like New York, Washington D.C. and Los Angeles have had similar reports.
"I immediately ordered a box of masks online after I heard of the first U.S. case," said Tina Liu, a Chinese student at the University of Washington, not far from Seattle.
The virus has killed 80 people in China and infected thousands, sending authorities scrambling to contain the outbreak. Wuhan, the city where it began, has been effectively quarantined along with 17 other cities, impacting China's economy and 50 million people directly.
Five cases have been reported in the U.S. American health officials said there are 110 people under investigation across 26 states as the outbreak continues.
While the masks are the most visible precaution during outbreaks, they aren't the most helpful, according to health experts.
"There's little harm in it," Eric Toner, a scientist at Johns Hopkins Center for Health Security, told Business Insider. "But it's not likely to be very effective in preventing it."
The Centers for Disease Control and Prevention said the best precautions are to wash your hands with soap and water, avoid close contact with people who are sick and clean and disinfect frequently touched objects and surfaces.
On Monday, the State Department upgraded its travel advisory for Americans traveling to China, urging them to reconsider their plans. The agency said it will evacuate all non-essential U.S. personnel and their families from Wuhan on Wednesday.
Some U.S. citizens will also be evacuated, the State Department said. All passengers will be screened for coronavirus symptoms before being allowed to depart China.