Bitcoin surged past US$17,000 ($24,900) on Thursday as the frenzy surrounding the virtual currency escalated just days before it starts trading on major US exchanges.
Bitcoin has gained more than US$5,000 ($7,323) in just the past two days.
The world's biggest cryptocurrency is surging on expectations that new bitcoin derivatives products expected to begin trading this month will boost mainstream demand.
Some of the world's biggest brokerages criticised those plans on Wednesday, telling regulators the contracts have been rushed to market without enough due diligence.
Bitcoin has jumped this year to more than 1,500 per cent and its market capitalisation to US$274 billion ($401b).
"This is irrational exuberance," Royal Bank of Scotland Chairman Howard John Davies said in an interview on Thursday. "This is a very, very unusual market, that shows we're not in a normal two-way trading market."
Davies agreed with the brokerages' concerns that exchanges which are set to offer bitcoin futures and options have failed to get enough feedback from market participants on margin levels, trading limits, stress tests and clearing. Those warnings were laid out in an open letter via the Futures Industry Association on Wednesday.
At the same time, there are fresh concerns about the security of bitcoin and other virtual currencies after NiceHash, a company that mines bitcoin on behalf of customers, said it is investigating a breach that may have resulted in the theft of about US$70 million ($102m) worth of bitcoin.
Research company Coindesk said that a wallet address referred to by NiceHash users indicates that about 4,700 bitcoin had been stolen. NiceHash said it will stop operating for 24 hours while it verifies how many bitcoin were taken. Wallet is a nickname for an online account.
At the start of the year, one bitcoin was worth less than US$1,000 ($1,464).
Futures for bitcoin will start trading on the Chicago Board Options Exchange on Sunday evening and on crosstown rival CME Group's platforms later in the month.
That has increased the sense among some investors that bitcoin is gaining in mainstream legitimacy after several countries, like China, tried to stifle the virtual currency.
Bitcoin is the world's most popular virtual currency. Such currencies are not tied to a bank or government and allow users to spend money anonymously. They are basically lines of computer code that are digitally signed each time they are traded.
A debate is raging on the merits of such currencies. Some say they serve merely to facilitate money laundering and illicit, anonymous payments. Others say they can be helpful methods of payment, such as in crisis situations where national currencies have collapsed.
Miners of bitcoin and other virtual currencies help keep the systems honest by having their computers keep a global running tally of transactions. That prevents cheaters from spending the same digital coin twice.
Online security is a vital concern for such dealings.
In Japan, following the failure of a bitcoin exchange called Mt Gox, new laws were enacted to regulate bitcoin and other virtual currencies. Mt Gox shut down in February 2014, saying it lost about 850,000 bitcoin, possibly to hackers.