The push comes as physical cash use falls globally and authorities look to fend off the threat to their money-printing powers from bitcoin and efforts linked to Big Tech such as the Facebook-backed Diem, formerly Libra.

At the same time, central banks who have taken interest rates negative are looking at whether digital cash could be used to help implement the radical policy.

Wednesday's BIS survey of 65 central banks showed 86% were exploring the benefits and drawbacks of digital currencies, with some testing possible designs.

Emerging and developing economy central banks are more likely than those in major economies to issue central bank digital currencies (CBDCs), the survey showed.

The Bahamas became the first country to launch a general purpose CBDC, known as the Sand Dollar, in October.

A number of bigger countries have also been testing the waters, with China the most advanced.

A fifth of central banks from major economies that responded to the survey said issuing digital currencies was "possible" in the short or medium term, up from only one last year.

(Graphic: Increasing numbers of central banks looking at issuing digital currencies: )

The People's Bank of China expanded a trial of a digital renminbi to its three largest urban regions, which together contain 400 million people, in August..

ECB President Christine Lagarde said last week her bank was pushing on with its work on a digital euro, Sweden's E-Krona is progressing and U.S. Federal Reserve chief Jerome Powell has said it is carrying out experiments for a digital dollar.

But there are still hurdles to overcome.

The BIS survey showed over a quarter of central banks do not currently have the authority to issue a CBDC and about 48% remain unsure. Around 60% see themselves as unlikely to issue any type of digital currency in the short or medium-term.

As a whole, though, "central banks are moving into more advanced stages of CBDC engagement, progressing from conceptual research to practical experimentation," the survey said.

(Graphic: Central bank digital currencies across the world Central bank digital currencies across the world: https://graphics.reuters.com/CENBANKS-DIGITAL/oakpejoervr/chart.png)

(Graphic: Reasons why central banks are looking at digital currencies: )

(Reporting by Marc Jones; Editing by Catherine Evans)

By Marc Jones and Tom Wilson