Bitcoin has blasted to another all-time high of just over $US17,750 ($A24,850), up 8 per cent on opening, as concerns grow over the risks of investing in the highly volatile and speculative instrument.

The cryptocurrency’s staggering price rises – more than 1700 per cent since the start of the year – have driven worries that the market is a bubble that could burst in spectacular fashion.

Bitcoin has climbed more than 77 per cent so far in December alone, putting it on track for its best month in percentage terms since December 2013.

On Friday it reached as high as $US17,752.99 ($A24,854.19) on the Luxembourg-based Bitstamp exchange.