FRANKFURT/NEW YORK (Reuters) - Warren Buffett's Berkshire Hathaway Inc has amassed a $1 billion stake in Germany's Munich Re, boosting its already large exposure to the reinsurance sector even as it prepares to complete its biggest acquisition.

Munich Re said Berkshire's stake rose on January 18 to 3.045 percent, just above the level at which such holdings must be disclosed.

"Warren Buffett is an expert at assessing risk qualitatively and has been in this business a long time," said Andy Kern, who teaches Buffett's strategies at the University of Missouri at Columbia and writes the Berkshire Ruminations blog. "It may also be he finds the stock cheap."

Berkshire owns General Re and is the world's third-largest reinsurer. Its Munich Re stake was revealed 11 months after Berkshire injected 3 billion Swiss francs ($2.88 billion) into Swiss Re, after the world's second-largest reinsurer wrote down large sums of illiquid assets.