Bitcoin loses 30 per cent value in a week

Bitcoin has tumbled more than 7.5 per cent to below $US4500 ($A6,174), knocking off nearly a third in value of the world's best-known cryptocurrency's losses within a week as a selloff in digital currencies intensified across the board.

Other cryptocurrencies also fell sharply, with Ethereum's ether losing 10 percent and Ripple's XRP down 13 per cent in a largely sentiment-driven slide.

Bitcoin is now trading at $US4354.20 ($A5,974.20), its lowest level on the Bitstamp exchange since October 2017.