Japanese carmakers Toyota and Honda have delayed plans to restart production, saying that they cannot get the parts they need.
Toyota will not restart production before 26 March. Honda Motors says it has extended a production shutdown until at least 27 March.
The firms have halted operations after Japan was hit by a deadly earthquake and tsunami.
Analysts said the shutdown would cost companies millions of dollars a day.
A spokeswoman for Honda said that the company now expects delivery of new vehicles in Japan to be delayed.
Assembling a car requires thousands of parts to be put together. These are provided by different suppliers.
Most of the parts are shipped to the manufacturers a short time ahead of the assembly line requirements, analysts said.
This means that most car factories have relatively low inventories, which can create shortages in supply.
Until the supply chain is sorted out, analysts warn that plants will not be able to operate at full speed and there may be patchy production across the country.
"Each supplier has to be able to reach the levels before the devastation to reach the full production plan," said Vivek Vaidya of Frost & Sullivan.
Manufacturers of Japanese cars in other countries are not so severely affected by the shortage of parts.
Paul Ormond of Honda UK said the firm's site in Swindon was not running at full production at present and therefore did not need so many components.
"We will probably be building 160,000 cars with the potential production capacity of 250,000, so that will actually mean we don't need to have a full inventory until we get to that level, which won't be for another year to 18 months," he told BBC News.
To get back to full speed, Japan's car manufacturers have not only got to overcome their own issues, but also wait for external factors to get sorted.
To begin with, they need uninterrupted power supplies, which analysts say will take some time given the situation at the Fukushima Daiichi plant.
"A significant percentage of Japan's electrical generating capacity has been taken offline, and is unlikely to be restored soon," said Aaron Bragman of IHS Global Insight.
To make matters worse for the manufacturers, a shortfall in power supply in one part of Japan cannot be easily replenished by transferring power from another part of the country.
Different power grids in Japan function at different frequencies, making it difficult for power to be transferred.
"The issues with the Japanese auto industry are quite serious," he said
"The situation is unlikely to return to normalcy any time soon."