Warren Buffett's Berkshire Hathaway has boosted its stakes in Japan's five largest trading houses to 7.4%.

The billionaire investor said he may invest more in the country.

Those companies are Itochu Corp, Marubeni Corp, Mitsubishi Corp, Mitsui & Co and Sumitomo Corp.

Berkshire has been increasing stakes in those companies starting on Buffett's 90th birthday in August 2020, when he disclosed owning 5% stakes in each company.

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At that time, the investments were worth more than $6 billion.

Berkshire reported increasing the stakes to more than 6% in November.

Buffett, 92, said in an interview with Asian news outlet Nikkei that he was "very proud" of the investments and would meet with the trading houses this week to discuss their businesses.

"We would love it if any of the five would come to us ever and say, 'We're thinking of doing something very big, or we're about to buy something, and we would like a partner or whatever,'" Buffett said.

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Berkshire does not invest in other Japanese companies, but Buffett said "there are always a few I'm thinking about."

The companies trade in a wide variety of materials, products and food, often serving as intermediaries, and provide logistical support.

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They are also deeply involved in the real economy in such areas as commodities, shipping and steel.

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Buffett's conglomerate owns dozens of businesses, including the BNSF railroad, Geico auto insurance, and consumer, energy and industrial companies, as well as stocks such as Apple, Occidental Petroleum and Bank of America.

Reuters contributed to this report.