Production of cars in Japan by Toyota fell by 63% in March compared with the same month last year.
Production has been disrupted since the earthquake and tsunami on 11 March and the company is facing shortages in supplies of parts.
The BBC reports factories have restarted but are working at a reduced output. The company says output won't return to normal till the end of 2011.
It has also announced more cuts in production at its factories in Asia.
Plants in eight Asian countries, including Thailand and India, will operate at 50% capacity from 25 April to 4 June.
The company has already announced that its factories in China will operate at 30-50% of capacity until 3 June.
Toyota's British plant will work the equivalent of three half-days a week in May.
Nissan production slumps too
Meanwhile, Nissan Motors has announced that output at its Japanese plants slumped by 52% in March compared with the same month last year.
Credit ratings agency Standard & Poor's predicts that the shortage of parts will be resolved by July but that power shortages in Japan, which are expected to continue during the northern summer, will prevent production from returning to normal until at least October.