Bitcoin dropped back below $40,000, erasing almost all the gains sparked by optimism about US President Joe Biden's executive order to put more focus on the crypto sector.

The largest cryptocurrency declined as much as 7.2 per cent to $38,894 on Thursday, falling for the first time in three days.

Most of the top cryptocurrencies were down at least slightly in the 24 hours to 4:15 p.m. Hong Kong time.