Ford has not received financial help from the government
Ford, General Motors, Toyota and Nissan have reported sharp drops in US vehicle sales as consumers remain reluctant to make expensive purchases.
GM's sales plummeted 53% in February from a year earlier, Ford's fell 48%, Toyota's dropped 40% and Nissan's declined 37%.
Carmakers around the world have been hit hard by the global downturn.
Earlier, Toyota, the world's biggest carmaker, said it was seeking a state loan to help its car financing unit.
US carmakers General Motors and Chrysler have received $17.4bn from the US government, while Ford has not been bailed out by the state.
"In our view, we are in an automotive depression," said Standard & Poor's equity analyst Efraim Levy.
"Shell-shocked consumers fearful for their jobs, the value of their homes and stock market assets are wary of making the sizable discretionary purchases."
GM said that total February sales were at their lowest level for the month since 1967.
GM's chief sales analyst Mike DiGiovanni said: "These are obviously unsustainable levels and will cause almost every major automaker across the world to seek government aid."
Toyota said that its car financing unit, Toyota Financial Services, was in talks with the government-backed Japan Bank for International Co-operation.
Local media reports said that it had applied for a 200bn-yen ($2bn; £1.45bn) loan. However, Toyota said no details had been decided.
Toyota has suffered from falling demand in the downturn
Toyota has said it expects to report its first annual loss since 1950.
The Japan Bank for International Co-operation helps to promote the competitiveness of Japanese companies overseas.
Japan's Finance Ministry said earlier on Tuesday that it would provide an additional $5bn to the bank from its foreign exchange reserves to help companies weather the economic downturn.
'Not in danger'
Toyota Financial Services does 70% of its business in the US, where the credit crunch has made it harder to offer financing and the economic downturn has hit demand for vehicles.
General Motors' financing arm, GMAC, has been hit by losses and has received a $6bn bail-out from the US government.
Analysts said that the news did not mean that Toyota was in trouble.
"Toyota is not in danger. It's out to get the lowest price for funding that the strength of its credit can get," said Yasuaki Iwamoto, an analyst at Okasan Securities, told Reuters news agency.
"On the balance sheet, it doesn't matter if the funds are private or public."
Reports also said that Nissan was considering various types of government aid.
Toyota ended GM's 77-year reign as the world's largest carmaker last year, as its sales surpassed its US rival.