Billionaire investor Warren Buffett celebrated his birthday with a $6.7 billion investment in a handful of companies in Japan. His Berkshire Hathaway Inc. purchased minority stakes in Japan's top-five trading outfits.

Berkshire Hathaway said it had bought stakes of roughly 5 percent in Itochu Corp., Mitsubishi, Mitsui Group, Marubeni Corp. and Sumitomo Corp. The five companies, which are known as "sogo shosha" or "general trading companies" contribute a substantial amount to Japan's gross domestic product. They operate several businesses in large industries such as energy, manufacturing and advanced technologies.

Based on the five companies' closing share prices Monday, Berkshire Hathaway's latest investment is estimated to be valued at a combined $6.7 billion. In a statement published earlier Buffett, 90, said he was very much delighted with the new investment as Berkshire Hathaway could participate in the future growth of Japan and the companies.

Historically, Japan companies have not always been open to foreign direct investments. However, Buffett's influence in Japan's business culture places him and his company in a different and more positive light with many in Japan.

Following the announcement, the share prices of the five companies rose by varying degrees Monday. The price rises - between 4 percent and 10 percent - also helped the Nikkei 225 index climb by as much as 1 percent.

Berkshire Hathaway said it planned to hold on to the stakes and considered them long-term investments. The company added it intended to increase the size of the holdings in each company to as much as 9.9 percent - depending on their performance.  

The latest stake purchases are among Berkshire Hathaway's more significant investments in Asia - apart from its holdings in China electric carmaker BYD.

Analysts said the investment underscored Buffett's intention of hedging against the weakening U.S. dollar. Buffett recently bought a stake in Barrick Gold, a company whose performance is closely tied to world gold prices and the movements of the U.S. dollar.