If tensions between the U.S. and North Korea escalate, a flood into safe havens will be the first warning sign, closely followed trader Art Cashin told CNBC on Wednesday.

“You’re going to have to watch those safe havens. If they begin to move very rapidly, then we’re going to go into a different kind of phase of trading here,” Cashin, UBS director of floor operations at the New York Stock Exchange, said in an interview on “Squawk on the Street.”

“[Safe havens] will give us the first warning if things are going to shift into the next gear,” he added.

U.S. stocks were lower Wednesday, one day after President Donald Trump warned North Korea that any threat to the U.S. would be met with “fire and fury.” On Tuesday, North Korea’s state media said the country was considering a strike on the U.S. Pacific territory of Guam with mid- to long-range missiles, according to Reuters.

Traditional global safe haven trades like gold and the Swiss franc rose Wednesday. Gold futures were on pace for its best daily performance since May 17, when they gained 1.8 percent. The CBOE volatility index (VIX), widely considered the best gauge of fear in the market, hit its highest level in one month. U.S. Treasury yields were lower.

Cashin pointed out that interestingly, investors are using the yen as a safe haven even though “it is one of the theoretical targets of any breakout.” The dollar weakened against the yen, which is often sought in times of geopolitical tension.

Wall Street is also seeing more caution than panic in Wednesday’s trade, Cashin said. He added there are no easy solutions to deal with North Korea’s threats. “Nobody’s got any good choices here,” he said.

Cashin reiterated his concerns about trading in 2017. He said in years that end in 7, markets tend to top out in August and sell off a few months later.