© Reuters. A bitcoin sign is seen during Riga Comm 2017 fair in Riga

By Jemima Kelly

LONDON (Reuters) - Bitcoin's vertiginous ascent showed no signs of abating on Monday, with the cryptocurrency soaring to another record high just a few percent away from $10,000 after gaining more than a fifth in value over the past three days alone.

The digital currency has seen an eye-watering tenfold increase in its value since the start of the year and has more than doubled in value since the beginning of October, lifted by the prospect of crossing over into the financial mainstream, amid a flurry of crypto-hedge fund launches.

It surged as much as 4.5 percent on Monday to trade at $9,721 on the Luxembourg-based Bitstamp exchange ( ), before easing back to around $9,600 by 1155 GMT.

Data compiled by Alistair Milne, the Monaco-based manager of the Altana Digital Currency Fund, showed U.S. bitcoin wallet provider Coinbase added 300,000 users between Wednesday and Sunday, during the U.S. Thanksgiving holiday. The total number of Coinbase users globally now stands at 13.3 million.

"The Coinbase data is evidence that adoption is not slowing down," Milne told Reuters. "Breaking $10,000 seems inevitable following the recent price action."

Bitcoin's price has been helped in recent months by the announcement that the world's biggest derivatives exchange operator CME Group (NASDAQ: ) would start offering bitcoin futures. The company said last week the futures would launch by the end of the year though no precise date had been set.

So far, institutional investors have largely stayed away from the market, viewing it as too volatile, too risky and too complex to invest other people's money into. But some say the launch of the CME futures could lure in more mainstream investors.

"Promises of bitcoin futures opening the door to institutional money are supercharging the price," said Charles Hayter, founder of cryptocurrency data analysis website Cryptocompare.

BIGGER THAN WAL-MART

The latest price surge brought bitcoin's "market cap" - its price multiplied by the number of coins that have been released into the system - to more than $163 billion, according to industry website Coinmarketcap.

The market cap of all cryptocurrencies, meanwhile, topped $300 billion for the first time, the site said, making their estimated market value greater than that of Wal-Mart (NYSE: ).

The staggering price increases seen in the crypto-market have led to multiple warnings from central bankers, investment bankers and other investors that it has reached bubble territory.

Some say that this could prompt regulators in the West to crack down on the market in a similar fashion to China, where bitcoin exchanges were shut down earlier this year.

"Regulators know the rewards of cryptocurrency and blockchain could be huge but (they) have more than one eye on the catastrophic ramifications if good governance, stability and control are not preserved," said David Futter, a fintech partner at law firm Ashurst, in London.

"If the carrot of self-regulation proves insufficient, the regulators will not hesitate to use their stick."

Bitcoin's biggest rival, ether - sometimes referred to as , the name for the project behind it - has seen even more stratospheric gains this year, up more than 6000 percent. It hit an all-time high just below $500 on Monday, with its market cap nearing $50 billion.