Bitcoin has moved another step towards mainstream investing with the start of trading on the huge Chicago Mercantile Exchange financial futures market, reports BBC.

It comes as the value of the digital currency approached $20,000 on Sunday, before drifting below $19,000.

Last week, Chicago's CBOE exchange began Bitcoin futures trading - bets on a future price - but CME is far bigger.

On Sunday, the chairman of UBS bank and former Bundesbank head Axel Weber joined the chorus of Bitcoin warnings.

"Bitcoin is not money," he said in an interview, and urged regulators to intervene.

Meanwhile the French finance minister, Bruno Le Maire, has called for the issue to be discussed at the G20 summit of major economies in April.

"There is evidently a risk of speculation. We need to consider and examine this and see how... with all the other G20 members we can regulate bitcoin", Maire told the French news channel LCI.

Bitcoin prices have surged this year: a single bitcoin stood at less than $1,000 in January and hit a record $19,783 on Sunday, according to Coindesk.