The tumble in cryptocurrencies that erased nearly $US500 billion of market value over the past month could get a lot worse, according to Goldman Sachs's global head of investment research.

Most digital currencies are unlikely to survive in their current form, and investors should prepare for coins to lose all their value as they're replaced by future competitors, Goldman's Steve Strongin said in a report this week. While he didn't posit a timeframe for losses in existing coins, he said recent price swings indicated a bubble and that the tendency for different coins to move in lockstep wasn't rational.

"The high correlation between the different cryptocurrencies worries me," Strongin said. "Because of the lack of intrinsic value, the currencies that don't survive will most likely trade to zero."

Today's digital coins lack long-term staying power because of slow transaction times, security challenges and high maintenance costs, according to Strongin.