The Reserve Bank chooses to call digital currencies such as bitcoin "cyber tokens" because they do not meet the requirements to be classified as money.

"We don’t use the term ‘cryptocurrency’ because it doesn’t meet the requirements of money in the economic sense of the stable means of exchange, a unit of measure and a stable unit of value," Reserve Bank deputy governor Francois Groepe said in Pretoria on Thursday.

"We prefer to use the word ‘cyber-token’."

Digital currencies such as bitcoin and ethereum are becoming increasingly popular, with regulators in some countries struggling to move fast enough to manage them.

The Reserve Bank has established a financial technology, or fintech, unit to review its position on private cryptocurrencies, and to help draw up an appropriate policy framework and regulatory regime.

"We want to ensure or establish whether there is still compliance with the relevant financial surveillance or exchange-control regulations," Groepe said.

The Bank is not the first to voice reservations about digital currencies.

In January, Nigerian governor Godwin Emefiele said investing in bitcoin was a "gamble", while Lesotho’s central bank said a month later that it would not offer any recourse to investors who lose money on cryptocurrencies.

Bank for International Settlements GM Agustin Carstens said in an interview with the German newspaper Boersen-Zeitung this week that he preferred to call these currencies "cryptoassets".