Cryptocurrencies plunged on Friday, with bitcoin at one point sliding below $8,000 and headed for its biggest weekly loss since December 2013, amid worries about a regulatory clampdown globally.

The currencies have come off their lows but analysts said the sell-off was probably not over.

This week's slump brought the total market value of cryptocurrencies down to around $400 billion, half the high it reached in January, according to industry tracker Coinmarketcap.com.

The market value of cryptocurrencies is calculated by multiplying the number of digital coins in existence by their price, although many question whether that is the right way to value them.

Bitcoin, the biggest and best-known crypto-currency, fell as much as 15 percent on Friday to a two-month low of $7,625 on the Luxembourg-based Bitstamp exchange. It clawed back some losses and was down around 5.6 percent at $8,498 in late New York trading.

The virtual currency is down by close to 25 percent this week and almost 40 percent in 2018. It surged more than 1,000 percent though in 2017.

For some market participants, bitcoin may be down, but it is not likely to fade.