Auto sales totalled 279,389 in March, the seventh-straight monthly decline, the Japan Automobile Dealers Association said Friday.
The 9.0 magnitude earthquake, Japan's biggest ever recorded, three weeks ago unleashed a tsunami that devastated swathes of the northeast coastline and hit the production of all of Japan's automakers.
Auto assembly and part manufacturing plants were damaged and companies were subjected to power shortages, causing a lack of components for both domestic and overseas car makers.
Auto sales, as measured by registrations of vehicles, are seen as a key indicator of consumer spending sentiment and are among the first data to be released each month in Japan.
The figures do not include sales of mini cars or trucks.