Bitcoin fell more than 5% on Friday, a day after topping $40,000 for the first time.
The world's most popular digital currency slid to as low as $36,618.36 on Bitstamp exchange, after reaching an all-time high of $40,402.46 in the previous session.
Rival cryptocurrency ethereum sank more than 10% to as low as $1,064.89.
Bitcoin has rallied more than 700% since a low in March. It topped $30,000 for the first time on Jan. 2, after surpassing $20,000 on Dec. 16.
Market participants had warned of a correction after the $40,000 milestone was reached.
Increased demand from institutional, corporate, and more recently retail investors has powered bitcoin's surge, attracted by the prospect of quick gains in a world of ultra-low yields and negative interest rates.
JPMorgan strategists wrote on Jan. 5 that the digital currency has emerged as a rival to gold and could trade as high as $146,000 if it becomes established as a safe-haven asset.
(Reporting by Kevin Buckland; Editing by Himani Sarkar)