Bitcoin plunges below $13,000 as 'Sharks Start to Circle'

Bitcoin plunged by more than $2,500 Friday to extend its four-day slide to 31 percent as the frenzy surrounding digital currencies faced one of its biggest tests yet.

The world's largest cryptocurrency sank below $13,000 as this week's selloff entered a fourth day with increasing momentum. (It had rebounded to over $15,000 by late morning) Other cryptocurrencies also tumbled, with bitcoin cash crashing 35 percent and ethereum losing 23 percent over the past 24 hours, according to coinmarketcap.com.

The losses represent a major test for the cryptocurrency industry and the blockchain technology that underpins it, which have rapidly entered the mainstream in recent weeks. Bears cast doubt on the value of the virtual assets, with UBS Group AG this week calling bitcoin the "biggest speculative bubble in history." Bulls argue the technology is a game changer for the world of investment and finance. Both will be closely watching the outcome of the current selloff.

"The sharks are beginning to circle here, and the futures markets may give them a venue to strike," said Ross Norman, chief executive officer of London-based bullion dealer Sharps Pixley Ltd., which offers gold in exchange for bitcoin. "Bitcoin's been heavily driven by retail investors, but there'll be some aggressive funds looking for the right opportunity to hammer this thing lower."

Traders who bought the currency on futures exchanges using collateral may start facing margin calls following the price decline. Two venues launched products in recent weeks that required hefty security, with Cboe needing 44 percent to clear contracts, and the CME 47 percent. Brokers set safety nets even higher.

"There's no doubt people who got in on margin will face some pressure here," Norman said by phone from London. "The volumes weren't huge, so it won't be a major price driver, but for those caught on the wrong side it will hurt."

Crypto Mania

Many of the recent news stories and market moves connected to cryptocurrencies appear to carry hallmarks of the mania phase of a bubble. Long Island Iced Tea Corp. shares rose as much as 289 percent after the unprofitable Hicksville, New York-based company rebranded itself Long Blockchain Corp. Bank of Japan Governor Haruhiko Kuroda said on Thursday bitcoin isn't functioning like a normal means of payment and is being used for speculation.

Still, cryptocurrencies are attracting established players. Goldman Sachs Group Inc. is setting up a trading desk to make markets in digital currencies such as bitcoin, according to people with knowledge of the strategy. The bank aims to get the business running by the end of June, if not earlier, two of the people said.

Bitcoin was trading 17 percent lower at $12,775 at 8:16 a.m. New York time on Friday. It reached a peak of $19,511 earlier this month, and is still up more than 10-fold for the year.