"On and off production at limited capacity underscores the severity of parts shortage problems for Toyota," he said.
Toyota gets more than 90 percent of its auto components in Japan, according to Saito.
Toyota suspended all car production in Japan from March 14 to 26. Since late March it resumed limited production at a handful of plants. The tsunami disaster has resulted in a production loss for Toyota of 260,000 cars from March 14 to April 8.
The parts supply crunch has been felt around the world, from Malaysia to the U.K. to the United States. Some Toyota dealers in the U.S. said the popular hybrid Prius is in now in short supply due to high demand and factory outages in Japan after the quake.
Toyota said Monday it's inevitable that it will be forced to temporarily shut down all of its North American factories because of parts shortages. Apart from Toyota, Nissan and Ford Motor Co. have said several North American plants would be closed for some of April, and Chrysler CEO Sergio Marchionne has said his company will see disruptions.
Toyota's share price has fallen around seven percent since March 11 to close Friday at 3,340 yen ($39).
Moody's Investors Service warned this week it may downgrade Toyota's credit rating due to the financial fallout from suspended car production.