Bitcoin plunged by 30 percent to below $12,000 on Friday as investors dumped the cryptocurrency after its sharp rise to a peak close to $20,000 prompted warnings by experts of a bubble.

After falling to as low as $11,159, it recouped some losses to trade above $14,000 on the Bitstamp platform, down 9 percent on the day. It is down around 25 percent this week, its largest weekly loss since April 2013.

It capped a brutal week that had been touted as a new era of mainstream trading for the digital currency when bitcoin futures debuted on CME Group Inc, the world’s largest derivatives market on Sunday.

Friday’s fall bled into the U.S. stock market, where shares of companies that have lashed their fortunes to bitcoin or blockchain – its underlying technology – took a knock. Long Blockchain Corp, Overstock.com Inc, Riot Blockchain Inc and Marathon Patent Group Inc lost between 2 percent and 15 percent.