US investment king Warren Buffett’s Berkshire Hathaway has reported a sharp plunge in first-quarter earnings, hit heavily by insurance losses related to Japan’s earthquake-tsunami disaster. Net earnings fell 56 percent to US$1.51 billion from US$3.63 billion a year earlier for the diversified investment house, long a favourite with small investors. Floods in Australia, the earthquake in New Zealand and Japan’s massive earthquake-tsunami disaster have hit the company’s re-insurance arm, which was expected to take a loss from underwriting for the first time in nine years. But Mr Buffett also reported that Berkshire’s companies, which span the clothing and insurance sectors – and much more in between – were starting to feel more optimistic about the US economic recovery.