The rating agency said Toyota's financial and operating performance will worsen as a result of the disasters, which are causing major disruptions in auto parts supply and have forced Toyota and other automakers to halt production.

Toyota, the world's No. 1 carmaker, suspended production at all its 18 factories in Japan from March 14 to 26 due to parts shortages. Since March 28, Toyota has been running just two plants at limited capacity to make Prius and Lexus cars.

The disasters resulted in a production loss of 200,000 cars from March 14 to April 1, said Toyota spokeswoman Shiori Hashimoto.

Moody's said Toyota's long-term uncollateralized debt rating is currently Aa2. The rating agency said its review for possible downgrade will focus on Toyota's ability to restore production in Japan.

Japan's top business daily Nikkei said Wednesday that Toyota would resume auto production at most of its domestic plants as early as next week. The Asahi daily said Toyota would reopen the remaining plants under limited capacity. Hashimoto denied the reports.

Car sales in Japan plunged nearly 40 percent in March following the tsunami.