Hygienic masks designed to stop the spread of illnesses like coronavirus are swelling in price online after the Centers for Disease Control and Prevention warned that the respiratory illness could create severe disruptions in the U.S.

The U.S. government said Americans should prepare for a Covid-19 crisis on Tuesday as the illness continues to spread across the globe. Within 24 hours, online prices rose on some medical face masks meant to shield people from viral infections.

On Amazon, one pack of disposable masks that was priced at $125 on Sunday surged to $220 per pack on Wednesday, according to data from Keepa, which tracks price changes on Amazon.

Another pack of basic sanitary masks was priced at $4.21 in early January and gradually increased over time. By Tuesday, the pack of 100 basic masks more than tripled, reaching $14.99, Keepa found. A day later, the price jumped another $3 before the product was pulled from the marketplace.

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The U.S. government has not declared coronavirus a pandemic. It also isn’t suggesting that people go out and buy masks to protect themselves. Still, third-party sellers are attempting to monopolize on the fears that could spark growth in demand for both cheap and pricier masks.

WIRED reported Tuesday that the best-seller in Amazon’s “Medical Face Mask” category surged to four times the price. The product, listed by a company called Kidirt, has since been removed from the website. A third-party seller offering medical-grade N95 respirator masks hiked prices from $38 to $81 on Tuesday, according to Keepa data.

Amazon sent an email to sellers warning them about masks that were not in compliance with its Fair Pricing Policy, WIRED reports.

Amazon wasn't immediately reachable for comment about the price gouging, but it’s not the first time this has happened on the platform. The tech giant’s pricing policy caused a stir in 2017 when bottled water prices surged after Hurricane Irma hit.

It’s not uncommon for sellers to alter prices within a reasonable range on Amazon. However, the online retailer’s website warns that it will take down listings by ruthless sellers who hike prices above a fair range.

“If we see pricing practices on a marketplace offer that harms customer trust, Amazon can remove … the offer, suspend the ship option, or, in serious or repeated cases, suspending or terminating selling privileges,” the company’s policy states.

Reuters reported on Tuesday that Italian authorities are investigating rocketing prices for coronavirus masks and hand sanitizer online. So far, Italy has seen the biggest outbreak of the illness in Europe.

Follow Dalvin Brown on Twitter: @Dalvin_Brown.