Bitcoin surges back over $22,000 after 30 per cent drop

Bitcoin surged over US$16,000 ($22,733) on Boxing Day in a rebound from the cryptocurrency's worst week since 2013.

The world's largest and best-known cryptocurrency fell nearly 30 per cent on Friday from an all-time high of US$19,843 ($28,194) to US$11,159.93 ($15,855) - losing more than a quarter of its value in a single day.

As of Tuesday morning (Wednesday NZT), however, the digital currency was up again to more than US$16,000 ($22,733), according to the Daily Mail.

Bitcoin has risen more than tenfold this year and doubled in just seven weeks, but if the currency goes bust, chaos could spill into the stock market, experts have said.

Wells Fargo Securities head of equity strategy, Christopher Harvey, said people should pay close attention to spill over in 2018.

"There is a significant amount of froth in the cryptomarkets. We do think that if that froth comes out, it will start to spillover," he warned on CNBC's Trading Nation.

He added: "What we're worried about is froth coming out of that market, and that's starting to affect equities.

"You're seeing it a little bit, but just not to a large degree. And, it's something to watch out for in 2018."

Bitcoin and similar cryptocurrencies have seen wild price swings over the past week, which could be a sign of the bubble popping as more people get interested in the digital currencies.

While bitcoin investors and analysts believe the decline in its value was a natural correction after a heady run-up in prices, there have been further warnings from market regulators and central banks.

Banks in several countries, including Singapore, have warned against investing in cryptocurrencies, saying that recent surges are driven by speculation, and there is a high risk of a sharp fall in prices.

The Israel Securities Authority has said that it is moving to ban trading in cryptocurrency-based companies on the Tel Aviv market until transactions involving digital coins are legally regulated.

The vice-president of the European Central Bank has also expressed concern about the relentless rise in the value of bitcoin and the potential risk accompanying the trend.

US Federal Reserve boss Janet Yellen has said bitcoin is not money and called on banks to be certain their digital currency transactions adhere to anti-money laundering statutes.