OMAHA, Nebraska, April 30 -- Warren Buffett, Berkshire Hathaway's chairman and chief executive, said on Saturday that derivatives remain a potential "time bomb" in financial markets.

When answering a question about the derivatives exposure of the banks in Berkshire's portfolio, Buffett said he was not worried about the company's investment in Bank of America or Wells Fargo, but the level of derivative exposure at large banks remains "a great danger" if there's a discontinuity in the financial markets.

"Derivatives are still dangerous on a large basis," Buffett said at the company's annual shareholder meeting, often known as Woodstock for Capitalists, held at the CenturyLink Center in downtown Omaha of Nebraska, noting that a major attack on the country that severely disrupts the financial system would reveal dangerous derivative positions.

"It's still a potential time bomb in the system," he warned, adding that Berkshire will never engage in dangerous derivative positions involving collateral. In the past, Buffet has described derivatives as "financial weapons of mass destruction."

Buffet also said the company would not think about investing in largest banks. "If you take the 50 largest banks in the world, we wouldn' t even think about probably 45 of them," he said.

The annual meeting was livestreamed to the public on Saturday for the first time in Berkshire's history and it was also translated into Mandarin in real-time, indicating the company's increasing interest in China. Around 40,000 investors all around the world came to Omaha to attend this year's meeting, about 3,000 of which were from China, according to local media.

The highlight of the annual gathering was the Q&A session, in which Buffett and his partner Charlie Munger took questions from shareholders, analysts and journalists about everything ranging from Berkshire, the stock market, the economic outlook to investment philosophy for around six hours.