The price of Bitcoin dipped by almost 6% overnight, bringing its losses for the week to more than 23%.
The value of the cryptocurrency peaked in December 2017 at almost $20,000 but it now sits at around $4,200 - a 78% slump.
The fall follows a sudden plunge last week that shook bitcoin out of a period of relative stability, where prices had hovered around the $6,500 mark for several months.
Bitcoin is now at its lowest level since October 2017.
Ripple's XRP and Ethereum's ether, the second and third-largest digital coins, fell as much as 14% and 16% respectively this week, before clawing back some losses.
Traders and market makers blame bitcoin's slide on heavy selling at leveraged exchanges in Asia such as Hong Kong-based OKEx and Bitmex.
Few exchanges in the West lend bitcoin to traders, making the Asian venues popular with speculators.
Others blame fears that last week's "hard fork" in bitcoin cash, where a software upgrade split the fourth-biggest coin into two separate currencies, could destabilise others.
The price of bitcoin tends to be sensitive to debates over how its underlying network evolves.
Last year the suspension of hard fork planned by major developers and investors proved a major catalyst to its breakneck rise.