A sharp bitcoin sell-off on Friday saw the crytocurrency lose 30 per cent of its value at one point as its losing streak stretched to four days.

Bitcoin fell as low as $11,159 US on Friday before it regained some ground to trade above $14,000 US on the Bitstamp platform, for a loss of nine per cent on the day.

For the week, bitcoin is down around 25 per cent.

In mid-November, bitcoin was trading at less than $6,000 US. At the start of the year, it was under $1,000.

The cryptocurrency has been notoriously volatile, with a significant crash every quarter. Yet this week has been a particularly unstable. The weekly performance is already the worst one-week return for bitcoin since 2013.

"A manic upward swing led by the herd will be followed by a downturn as the emotional sentiment changes," said Charles Hayter, founder and chief executive of industry website Cryptocompare in London. "A lot of traders have been waiting for this large correction."

"Most of it is unsophisticated retail traders getting burned badly," said Stephen Innes, head of trading in Asia-Pacific for retail FX broker Oanda in Singapore.

"It is a buyer-beware time," said J.J. Kinahan, chief market strategist at TD Ameritrade in Chicago.