The price of a single bitcoin passed the $13,000 US level for the first time on Wednesday, a gain of $1,000 in less than a day.

The value of the world's most famous cryptocurrency is soaring, up more than 1,500 per cent in the past 12 months alone.

Bitcoin is seeing a flurry of interest even as regulators and mainstream investors are warning it has become a speculative bubble.

"We are in the throes of a bubble market, and one of the characteristics of a bubble market is that there is no way to know when the bubble will burst," said Mick McCarthy, CMC Markets' chief market strategist.

Despite the dire warnings, the currency got new legitimacy this week when U.S. regulators permitted various exchanges to start trading in bitcoin derivatives — securities that will allow investors to bet on or against the value of bitcoin without owning it themselves.

"There is a lot of money flowing into bitcoin right now, mostly motivated by 'fear of missing out' and greed," said Leonhard Weese, president of the Bitcoin Association of Hong Kong.

With files from Reuters