High bond valuations can go on for a long time, BlackRock's Rieder says

'Biggest bond bubble' ever?

While there may be legitimate concerns about a bond market bubble, it doesn't appear that the bubble will pop anytime soon, BlackRock's Rick Rieder suggested Thursday.

That's because bubbles usually blow up when there is more supply than demand, he said.

"I think there is a legitimate point about where … developed markets rates are relative to what is fundamental value," the chief investment officer of global fixed income at BlackRock said in an interview with CNBC's "Power Lunch."

"The thing that is extraordinary about today's market is that demand still outstrips supply. So while some of these valuations are high ... that can go on a long time."

Paul Singer's Elliott Management warned in a recent letter to investors that the bond market is "broken" and that it is now experiencing the biggest global bond bubble in history.

Among the things that could cause an irrational exit from the bond market could be a significant move higher in inflation or more fiscal initiatives faster, Rieder said.

Right now, he believes the U.S. will still be in a low interest rate dynamic for a while and generating return in fixed income markets will continue to be challenging.

Therefore, he believes it's important for fixed income investors to diversify their portfolios.

"You are still getting paid substantially positive real rates in places like Brazil or Argentina or Mexico or Indonesia," Rieder said. "As long as the dollar stays reasonably contained, as long as growth is moderate but growing, I think emerging markets will do well."

He also thinks money will flow into the equity market.

— CNBC's Kate Kelly contributed to this report.