"In terms of cryptocurrencies, generally, I can say nearly with certainty that they will come to a bad ending", Buffett said on CNBC, noting that he didn't understand Bitcoin and other blockchain-based digital assets.
"When it happens or how or anything else, I don't know", he added in an interview on CNBC's "Squawk Box" from Omaha, Nebraska. The stock-picker told CNBC he'd "be glad" to buy five-year put options on "every one of the cryptocurrencies".
Also on the show, Buffett's right-hand man, Charlie Munger, also blasted frothiness in bitcoin - and in venture capital funding.
Berkshire said Wednesday that it is expanding its 12-member board of directors by two and naming Gregory Abel and Ajit Jain to fill the spots. Mr. Jain, Berkshire's most important insurance executive, has been named vice chairman of insurance operations. Meanwhile, Jain, who's now executive vice president of National Indemnity, will be vice chairman of insurance operations.
"They've both got Berkshire in their blood", Buffett said.
"I actually would hope that we have somebody that's. already very rich - which they should be if they've been working a long time - and really is not motivated by whether they have 10 times as much money than they and their families can need or a 100 times as much", he said. "Why in the world should I take a long or short position in something I don't know about?"
Exchange operators such as CME Group and Cboe Global Markets have opened their platforms to allow bitcoin futures trading.
Bitcoin was marginally lower at 14,426 United States dollars in afternoon trading on Wednesday, according to prices listed by Coindesk.
Buffett's comments come a day after JPMorgan Chase Chief Executive Jamie Dimon said he regrets calling bitcoin a fraud, referring to comments he made at a banking conference in September.