Influential hedge fund manager Mike Novogratz is warning the bull run in the price of bitcoin isn’t built to last.

The value of bitcoin has increased nearly 50 per cent in the last week alone – and that is simply not sustainable, Novogratz told BNN in an interview.

“We’re in a speculative mania. There is absolutely no doubt this is a speculative mania. I think this will be the biggest speculative mania of our lifetimes, because it’s global,” he said. “Sometimes there’s 60, 70 per cent of the volume that happens in the crypto space coming out of Korea and Japan alone.”

In spite of bitcoin’s “cryptocurrency” moniker, Novogratz said he doesn’t think anything that moves as violently and as suddenly as bitcoin can possibly be put in the same category as the U.S. dollar or the British pound.

“Bitcoin really isn’t a currency. You can’t have a currency that’s this volatile. It’s got one use case right now, and it’s digital store of wealth, just like buying a piece of art. It’s like buying digital gold,” he said. “You don’t buy your fancy tie with gold, or your shoes.”

Novogratz made his name at Fortress Investment Group and was listed as a billionaire by Forbes in 2007 and 2008. The fund manager is launching a US$500 million fund to invest in cryptocurrencies but warns that speculators have to be selective as it’s unlikely all of the hundreds of different bitcoin-like digital currencies – also known as tokens – will thrive or even survive.

“There [are] a lot of frauds that are going to get washed out,” he said. “There are some tokens that are going to go to zero.”

“I’d stay with the blue chips unless you’ve really done a lot of your own work. In any of these speculative frenzies when there’s a huge tailwind, there are a lot of fly-by-night guys just trying to make a dollar.”

Update: Novogratz announced on Dec. 22 that he is shelving plans to launch a cryptocurrency hedge fund.