Berkshire Hathaway Inc has bought a five-percent stake in each of Japan's five biggest trading houses, together worth over six billion U.S. dollars, marking a departure for Chairman Warren Buffett as he looks beyond the United States to diversify his conglomerate.

The long-term investment in Itochu Corp, Marubeni Corp, Mitsubishi Corp, Mitsui & Co Ltd and Sumitomo Corp could see the stakes rise to 9.9 percent, Berkshire said on Sunday, Buffett's 90th birthday.

The investment will help reduce Berkshire's dependence on the U.S. economy, which in the last quarter contracted the most in at least 73 years as the COVID-19 pandemic took hold. Many of its businesses have struggled, including aircraft parts maker Precision Castparts from which it bore a 9.8 billion U.S. dollars writedown.

Why Japan?

Buffett's choice of Japan, however, surprised market players as trading houses have long been far from investor favorites. As well as significant exposure to the energy sector and resource price volatility, tangled business models involving commodities as varied as noodles and rockets have long been a turn-off.

"Their cheap valuation may have been an attraction," said Norihiro Fujito, chief investment strategist at Mitsubishi UFJ Morgan Stanley Securities in Tokyo.

Firms' shares often rise when Buffett discloses investment, reflecting what investors view as his imprimatur. On Monday, Marubeni and Sumitomo ended up over 9 percent, followed by Mitsubishi and Mitsui at over 7 percent. Itochu rose 4.2 percent to a record high.

Itochu Chairman Masahiro Okafuji in an emailed statement welcomed Buffett's interest in Japanese trading house stocks, which he said have lagged global financial markets, adding the investment "will be a catalyst for revitalizing the industry."

Most of Berkshire's operating businesses are American, though it has acquired a handful of foreign companies including Israel's IMC International Metalworking and German motorcycle apparel retailer Detlev Louis.

Additional investments in Japan could also help reduce Berkshire's cash pile, which ended June at a record 146.6 billion U.S. dollars.

(With input from Reuters)