The U.S. stock market should not be trading at record highs because the data on fund flows don't support the moves, said Larry Fink, chairman and CEO of BlackRock (BLK), the world's largest asset manager.
"I don't think we have enough evidence to justify these levels in the equity market at this moment," Fink said Thursday on CNBC's " Squawk Box ."
He said the recent rally has been supported by institutional investors covering shorts, or bets that stocks would fall, and not individual investors feeling bullish.
"Since Brexit, we've seen ETF flows almost at record levels ... $18 billion of inflows," Fink said. "However, in the mutual fund area, we're continuing to see outflows."
What that tells you is retail investors are pulling out, he said. "You're seeing institutions who were short going into Brexit ... all now rushing in to recalibrate their portfolios."
Besides the stock mutual fund outflows, Fink said he's been seeing huge inflows in fixed-income products. "So you're seeing a risk-off trade, as we call it, around the world."
"I would not be surprised — I'm not predicting it — if somebody told me the 10-year Treasury is at 75 basis points, I would not be surprised ," Fink said.
There's also $55 trillion in cash on the sidelines, he estimated. "You're seeing a massive reservoir of cash building up."
Fink said extraordinary central bank asset purchases has been inflating stocks prices.
"I don't think we should be at new [stock] highs," he said. "All the stock repurchases, you're seeing this reduction in investable assets."
The Dow Jones industrial average (Dow Jones Global Indexes: .DJI) closed at an all-time high Wednesday, notching a four-day winning streak. The S&P 500 (^GSPC) set all-time intraday highs, but closed barely above breakeven.
Fink noted, however, there's not enough information to say whether the stock market is overvalued at these levels. Earnings season will be key to answering that question, he added. "If corporate earnings are going up, then it may validate these [market] prices."
On the U.K. vote to leave the European Union , Fink said he still believes Britain faces a "short-term" recession because of the Brexit vote, despite the Bank of England's surprise decision on Thursday to keep interest rates unchanged.
In his last appearance on "Squawk Box" in June, before the Brexit referendum, Fink said he was nervous about a vote for Britain to leave the European Union. But he argued at the time that either way Britain needs to "create opportunity" to ease concerns people have about their economic future.