The head of the World Bank compared cryptocurrencies to "Ponzi schemes", the latest financial voice to raise questions about the legitimacy of digital currencies such as Bitcoin.

"In terms of using Bitcoin or some of the cryptocurrencies, we are also looking at it, but I'm told the vast majority of cryptocurrencies are basically Ponzi schemes," World Bank Group president Jim Yong Kim said on Wednesday at an event in Washington.

"It's still not really clear how it's going to work."

The development lender was "looking really carefully" at blockchain technology, a platform that uses so-called distributed ledgers to allow digital assets to be traded securely.