Buffett's 10 pct BYD stake purchase completed, value quadruples.

Warren Buffett's Berkshire Hathaway Inc. completed the purchase of a 9.89 percent stake in Chinese electric car maker BYD (Build Your Dreams), after the China Securities Regulatory Commission approved the purchase, BYD told the stock exchange today, Bloomberg reported.

Berkshire's MidAmerican Energy Holdings unit agreed to make a $230 million investment in BYD in September. Now that investment is worth about $1 billion in paper as BYD has surged in the Hong Kong market on publicity from Buffet's support.

Since the intent to make the purchase was announced last fall, BYD's stock has jumped about 400 percent, CNBC noted. The electric vehicle maker's stock has also been boosted by an increasing demand for its electric vehicles.

BYD is behind the first mass-produced plug-in hybrid, the F3 DM, which began selling in December.