Veteran investor Jim Rogers is already predicting the worst bear market for stocks in his lifetime. And that's before you figure in a trade war.

"The next bear market is going to be the worst in my lifetime — just because of the debt — but if we also have a trade war, it's going to be worse than a disaster," Rogers, the 75-year-old chairman of Rogers Holdings Inc, said in a Moscow interview. "I'm extremely concerned. I've read enough history and been through enough markets to know that trade wars are usually a disaster."

Rogers spoke as the prospects for a full-blown trade spat looked to be increasing. President Donald Trump plans as much as $60 billion of tariffs on Chinese products as early as this week to swat Beijing for alleged intellectual-property theft, according to two people familiar with the matter. Meanwhile, China is preparing to hit back with levies aimed at industries and states where Trump's supporters are found, the Wall Street Journal reported, citing unidentified people familiar with the matter.