"Whether or not you believe in the merit of investing in cryptocurrencies, real dollars are at work here and warrant watching," the report said.
However, Sheba Jafari, a technical strategist at Goldman Sachs, warned the bubble could burst and the price could eventually fall to below US$3,000 (NZ$4193).
But Aaron Lasher, co-founder of Breadwallet, is more optimistic - he predicts the value of bitcoin will keep on rising over the next five years.
"Are cryptos in a bubble? Yes, absolutely," he told MarketWatch.
"Is that a bad thing? Not necessarily.
"The long-term trend is up, however, so past bubbles look less impressive in the rearview mirror.
"Do I know how high this bubble will go? Will I be selling any bitcoin before, during, or after the bubble? No."
Meanwhile, the price of ethereum, the rising star of the cryptocurrency world, has risen to a high of US$394.32 (NZ$551.10).
The price rise of bitcoin, litecoin and ethereum puts the overall value of the cryptocurrency market at record US$170 billion (NZ$237b), coindesk reports.
They add the price of bitcoin is now up more than 350 per cent this year.
Thinking of investing in bitcoin?
The Telegraph's Technology Editor, James Titcomb, warns: "While the party may continue for a while, it's just as likely to end spectacularly."