Days after the Centers and Disease Control and Prevention warned about a potential coronavirus pandemic and spread of the virus through communities in the United States, prices for protective face masks have skyrocketed.

After some sellers on Amazon marked up face masks to nearly four times their regular price, the site warned sellers that price gouging could get them thrown off the website, CNET reported.

This week, a box of 100 regular face masks was being sold for $15, almost quadruple its price just a few weeks ago and a 20 pack of 3M particulate respirator masks rose from $17 to $70. A 10-pack of 3M N95 respirators had gone up to $99.99 from $18.20 a month ago, CBS News reported.

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"Sellers set their own product prices in our store and we have policies to help ensure sellers are pricing products competitively. We actively monitor our store and remove offers that violate our policies," an Amazon spokesman said in a statement, according to CNET.

By Wednesday, Amazon had already sold out of some brands, CBS reported.

Face masks sold at a 7-Eleven store at Dallas-Fort Worth International Airport had risen from $1.99 to $6.99, KTVT-TV reported. 7-Eleven later said the price had been “corrected” and was now back to $1.99, according to a statement to KTVT, .

“While franchisees are independent contractors and as such set the prices in their stores, 7-Eleven has contacted the franchisee that operates this store to address this issue. The franchisee has informed us that the price of this product has been corrected and is now $1.99,” the statement said.

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Prestige Ameritech, the largest manufacturer of face masks in the U.S. said it can't keep up with the demand.

"It's a madhouse," executive vice president of the company, Mike Bowen, told CBS.  "We are going as fast as we can."

"It's a madhouse. We are going as fast as we can."

— Mike Bowen, Prestige Ameritech

In Italy, which has seen the largest outbreak of the virus in Europe, authorities are investigating reports of price gouging.

“We have decided to open an investigation after media reports of the insane prices fetched up by these products (masks and gels) on online sales websites in the last two days,” Milan deputy chief prosecutor Tiziana Siciliano told Reuters.

Many pharmacies in the country say they have run out of masks and hand sanitizer, leaving consumers with online purchases.

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This is all despite the fact that the CDC doesn’t recommend face masks for people without symptoms. Instead, it stresses handwashing and not touching your eyes, nose or mouth.