Warren Buffett doubles down on Apple

Warren Buffett has been on a Apple stock buying spree.

The billionaire investor told CNBC on Monday that his Berkshire Hathaway investment firm has more than doubled its share in the Cupertino, Calif.-headquartered tech giant to 133 million shares, or about $17 billion.

Berkshire Hathaway had 57 million shares in Apple in the fourth quarter, according to a securities filing from earlier this month. After Jan. 1, it bought 120 million Apple shares.

The investment firm's holdings of Apple would amount to about 2.5% of the company. "We’ve spent a lot of money since Dec. 31," Buffett said on CNBC.  Apple's share price "has shot up since then," he said. "It’s at a price different than I would buy it now."

Apple (APPL) shares rose 0.2% to $136.93.  So far this year, Apple stock has risen 18%.

When CNBC's Becky Quick asked Buffett why he purchased the shares, he answered, "Because I liked it."

She noted that he is not traditionally an investor in tech firms. Buffett responded that Apple is more of a consumer product maker and that once consumers buy Apple they will likely remain a customer.

Buffett held up his own cellphone, which looked to be a Samsung feature phone. "There is a vast untapped market out there," he said. "86-year-old guys who haven’t got it yet."

Berkshire's net worth grew $27.5 billion, or 10.7%, in 2016 to $172,108 per Class A equivalent share, according to the Omaha, Neb.-based firm's annual shareholder letter released Saturday.

The company also bought more than $9 billion of airline stocks because Buffett believes airlines have increased their efficiency. After all the bankruptcies and consolidation in the industry, Buffett says the airlines are performing better and generally flying with their planes at least 80% filled.

At the end of 2016, Berkshire held 45.5 million shares of American, 60 million shares of Delta, 43.2 million shares of Southwest and nearly 29 million shares of United Continental.

On Kraft Heinz Foods' $143 billion bid to acquire Unilever, Buffett said that the deal fell apart because the European company wasn’t interested. It initially appeared that Unilever might be open to negotiating a deal, Buffett said, but once a rough offer was delivered it became clear the owner of Lipton and Hellman’s wasn’t interested.

Buffett's Berkshire Hathaway and 3G Capital abandoned Kraft Heinz Foods’ bid for the company because they were interested only in a mutually agreed upon tie-up, not a hostile takeover, he said.

The Associated Press contributed to this article.

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Follow USA TODAY reporter Mike Snider on Twitter: @MikeSnider.