"Tariffs are actually, we've had a lot of experience with them. They're an act of war, to some degree," Buffett said.

Donald Trump on Monday said that Canada and Mexico can't avert his sweeping tariffs, due to come into effect on Tuesday.

Warren Buffett is celebrating the successes of Berkshire Hathaway’s companies last year and in the 60 years since he took over a struggling New England textile company and began converting it into a massive conglomerate.