Supply shortages could be made worse by the fact that parts for masks and respirators are made in a variety of countries. More than 90 percent of surgical masks sold in the United States are produced overseas, according to the Department of Health and Human Services. Parts — or sometimes the final assembly — may be based not only in China and Taiwan but also in Japan, Vietnam, Mexico and Colombia.

“These countries could easily cut off our supply chain,” said Laurie Garrett, a policy expert and Pulitzer Prize-winning reporter who has written about the SARS, Ebola and other outbreaks.

With China’s pipeline to the outside world running dry, medical suppliers around the globe, including giants like Honeywell and 3M, are scrambling to find alternative sources. Both companies said through representatives that they were experiencing a surge in demand and were moving to ramp up production wherever they could.

Prestige Ameritech, a mask manufacturer in North Richland Hills, Texas, is among companies that received international orders as the coronavirus spread to 24 countries in the last few weeks, including from the governments of Hong Kong, Singapore and Taiwan.

“I have thousands of emails from people in Asia,” said Mike Bowen, the executive vice president. “Last week I sent over a million masks to China. That’s one thing I never predicted, that I’d be sending masks to China.”

Even the smallest producers are caught in the surge.

Pardam, a company in the Czech Republic that makes nanofibers, which trap micro-particles, almost ditched a sanitary mask prototype that it had tested last year because of tepid demand. But after the coronavirus hit, Pardam sold out of its stock of 2,000 masks within two days last week, and is turning to automation to increase production, said Jiri Kus, chairman of the Czech Association of Nanotechnology Industry, speaking on behalf of Pardam.