General Motors Co will only learn the impact of Japan's earthquake and nuclear crisis on its supply chain within a week or two, Chief Executive Daniel Akerson said on Friday, as shortages of components and other supplies deepen.

The largest U.S. carmaker is assessing possible bottlenecks that Japan's woes could cause for GM factories around the globe, Akerson told reporters in Sao Paulo. He is in Brazil to announce the opening of a third shift at GM's Sao Caetano do Sul plant.

I would say over the next week or two we will have a better understanding not only about what is happening in Japan but also where we are on an inventory basis around the globe, he said.

Plant shutdowns across Japan following the earthquake, tsunami and nuclear crisis risk limiting supplies of everything from semiconductors to car parts for manufacturers across the globe. Honda <7267.T> and Renault are curbing output as ruptured logistics, sagging confidence and energy shortages hamper operations.

GM's Opel unit in Europe called a 24-hour production stop for next Monday and an eight-hour halt next Friday at its plant in Zaragoza, Spain, due to the lack of an electronic item which had not arrived from Japan.

Akerson also said that the Japanese economic recovery was on solid footing shortly before the earthquake. He said the U.S. economy is having a reasonable revival, while Europe's recovery looks flattish.

GM shares rose 1.3 percent to close at $31.85 on Friday, below their November IPO price of $33.

The third shift in the Sao Caetano plant in Brazil, where sales are performing well, will allow production capacity to rise to 250,000 units a year from 200,000. Asked whether he was content with GM's third-place rank in Brazil sales, Akerson said no.

(Writing by Guillermo Parra-Bernal, editing by Matthew Lewis)