Berkshire Hathaway accumulated a 5.5 percent stake in IBM, Warren Buffett said on Monday, his biggest bet on the technology field that he has historically shunned.

Buffett, in a CNBC interview, said he bought about 64 million shares of IBM, which cost around $10.7 billion. Berkshire started buying the shares in March with a goal to build a $10 billion position, he said.

Buffett also said IBM did not know that he was building a stake, and that the company was finding out about his investment for the first time as he said it on CNBC.

According to Thomson Reuters data, a 5.5 percent position would tie Buffett with State Street Global Advisors for the largest stake in the company.

IBM shares rose nearly 1 percent in premarket trading.

(Reporting by Ben Berkowitz; Editing by Derek Caney)