Nissan CEO Carlos Ghosn says the massive earthquake that struck Japan last year turned from a nightmare into the company's "finest hour" as staff recovered from the magnitude 9 shock.

"Auto CEOs seem to be battling crises on many fronts," Ghosn said at this year's Automotive News World Congress in Detroit. "For Nissan the crisis [was] the magnitude 9 earthquake which struck the North East coast of Japan, that left 20,000 people dead or missing.

"It created a disaster for Japan on a scale unseen since World War Two. The nuclear power station was melting down and people thought we would shut, but the fighting spirit of our team was so strong. By mid-May, we were back to 80% capacity, by September, Nissan returned to unrestricted production. With the whole world watching, Nissan's employees turned a nightmare into a finest hour."

The Nissan chief also highlighted the floods in Thailand and "abnormally stunning" strength of the Japanese yen as crises in their own right, but insisted mergers were not the way forward for the industry to cope with them.

"Conventional mergers and acquisitions have not fared well, at least for the auto industry," he said. "Most of the marriages have ended in ruinous divorces [but] we have built the longest-surviving partnership in our industry.

"The number of skeletons through acquisitions and mergers have been numerous, so the only thing we keep is alliances and strategic partners."

Ghosn also attacked the extraordinary strength of the yen, saying nobody who examined the Japanese economy could understand why the currency continued to soar, increasing to the dollar for example, by 40%. "Even the Japanese government says it is wrong," he said.

"I consider it a very strong headwind which is bad for Japan - production is shifting to some low-cost countries - it is a pity for Japan."