(Bloomberg) — People across the globe are stockpiling facial masks to protect themselves from the new coronavirus, depleting online malls and store shelves from California to Beijing. Yet their efficacy against an outbreak that’s claimed more than 130 lives remains uncertain.

On Amazon and Alibaba, many shops peddling anti-virus masks had run out of stock as of Wednesday. Across China, Hong Kong and Singapore, people lined up for hours at stores and pharmacies hoping to secure dwindling supplies. People from San Francisco to Orlando said they were unable to find surgical masks at their usual outlets.

While the rush is global, Chinese people living abroad have been buying masks — especially the popular N95 variant made by 3M Co. — to send back to family members or resell them online, often via Tencent’s WeChat messaging app. Demand is only likely to increase — even though doubts have surfaced among the medical community about their effectiveness in curbing the disease, which some doctors say can spread through physical contact. The coronavirus, which first emerged in the central Chinese city of Wuhan, has infected more than 6,000 — more than the 5,327 cases officially reported in China during the SARS epidemic of 17 years ago.

“I’ve been running around town for days to buy masks,” said Liu Yan, a 36-year-old, who works in the cryptocurrency industry in Tokyo and said she scooped up 2,000 masks to send back to people in China without asking for additional money. She added she may stop buying soon because patient numbers were on the rise in Japan and she didn’t want to deprive locals of supplies.

What you need to know about the outbreak: QuickTake

While it’s still unclear how the 2019-nCoV virus is spreading, one confirmed channel is through direct contact with infected people — most likely coming into contact with respiratory secretions or virus-containing droplets from an infected person’s cough. It’s also possible the virus could be shed in other ways, including through the fecal waste of acutely infected people.

Good hand hygiene, including the regular use of an alcohol-based sanitizer, may be more effective than face masks at preventing transmission of the 2019-nCoV virus, said Peter Collignon, an infectious diseases physician and microbiologist at Australia’s Canberra Hospital.

China’s government has responded to the worsening shortage by cracking down on vendors who sell fake masks or overcharge online. Over 80 shops on e-commerce platform Taobao, run by Alibaba Group Holding Ltd., allegedly sold counterfeit 3M and N95 face masks, Chinese state-media reported Monday. The company said on its official Weibo account it removed shops found to engage in false advertising or price rigging. The e-commerce site said it sold 80 million face masks through Taobao within two days.

In Hong Kong, some store chains have begun restricting sales. Watsons said on its official Facebook account it would receive a limited supply on Jan. 30, then limit purchases to 50 masks per person on a first come first serve basis. People in the city who have tried to send masks to mainland China said their deliveries got bounced back without being given a clear reason.

3M said it’s increasing output and working with distributors to ensure sufficient inventory to meet demand and supply existing customers, according to a representative. Other factories are ramping up production. In Japan, plants that supply personal care company Unicharm Corp. have been working around the clock since Jan. 17 after orders increased ten-fold, according to spokesman Hitoshi Watanabe.

Meanwhile, the global mask stockpiling is spurring market speculation. Shares in surgical equipment maker Medtecs International Corp. have more than quintupled since the start of the year.