A key factor still to be determined is whether the Japanese ports from which the auto companies ship vehicles and parts will be able to resume operations soon.
Much of what the top three brands — Toyota, Honda and Nissan — sell in the United States is already made in North America. The question will be whether there are high-profit cars — such as Toyota's Lexus line or Honda's Acura brand, which are still made in Japan — that can't be shipped here.
A large batch of vehicles is already in transit, so inventories should not be a problem in the short term, said Michael Robinet, an analyst with IHS Automotive.
"A bigger issue would be if a factory was damaged so significantly that the automaker had to move production elsewhere while it rebuilt, especially for a key component such as an engine or transmission that is in short supply or is needed for production in the United States," he said.
But it will likely take the automakers several days to sort out what has happened to their facilities.
"It really is too early to tell what the longer term effects will be," he said.
Honda Motor Co. has shut three plants through Monday, including one where it makes the Fit sub-compact car and the top of the line Acura sedan that are exported to the United States. Its research center in Tochigi also was damaged, killing a 43-year-old man, and at least 30 other Honda employees were injured in the region.
"We are working very hard to assess the impact of this on our operations," said Jeffrey Smith, a Honda spokesman in Torrance.
He noted that more than 80% of what Honda sells in the United States, mostly Civics and Accords, are made here, as well as most of the parts that go into the vehicles.
But two factories in the area hit by the quake make engines and transmissions, and analysts said if they turn out to be critical export components, production in the United States could be disrupted.
Toyota Motor Corp. said it has closed four factories while it assesses if they suffered major damage, including the factory where it makes the small Yaris subcompact sedan and two Scion models. None of the vehicles are major sellers in the U.S.
Nissan Motor Co. said it has suspended operations through Sunday but did not report any significant damage as of yet.
"At this point it looks like mostly a temporary domestic issue for Japan," said Efraim Levy, an analyst at Standard & Poor's Equity Research.