Billionaire investor Warren Buffett warns if Starbucks Corp. founder Howard Schultz runs for president as an independent it could help Republican Donald Trump win a second term.

"If he ran as an independent, I think he would take votes away from any Democrat, including (former three-term New York City Mayor Michael) Bloomberg if he were running," Buffett told CNBC. “I think it would be a real mistake for him to run."

Buffett said he's not a "card-carrying Democrat but I never have been" but had voted for more Democrats than Republicans over the last 30 years.

He said he would support fellow billionaire Bloomberg for president.

Bloomberg is running as a Democrat, after being elected mayor as a Republican and as an independent.

"If Mike Bloomberg announced tomorrow that he's a candidate, I'd say I'm for him. I think he'd be a very good president," Buffett said.

"He and I disagree on some things ... but I think he knows how to run things," he added. "He's got the right goals for America. He understands people. He understands the market system. And he understands the problems of people" not involved in the market.