Auto production of Japan?s top automakers was interrupted after Riken Corp., a leading auto part supplier, was damaged by a powerful earthquake which hit the territory last Monday. The quake killed ten people in Japan and also damaged a huge nuclear plant in Kashiwazaki thus resulting to a radioactive water spill into the Sea of Japan, the Detroit News reported.

Riken’s Kashiwazaki facilities were damaged and several employees were injured by Monday’s 6.8-magnitude quake, according to Japanese media reports. Riken is Japan’s biggest manufacturer of piston rings and also makes sealing rings for transmissions.

According to an Associated Press report, the extent of the leak was initially understated, but plant operator Tokyo Electric Power Co. said that radiation levels did not pose any danger.

The Toyota Motor Corp., Japan’s biggest automaker, stopped production at its Japanese plants Wednesday after the said supplier of transmission and engine parts, sustained heavy damage at its facilities from the quake. Additionally, Toyota also cancelled one shift today and all production at its assembly and components plants in Japan on Friday. It could not say when its operations would be up and running normally, said the News.

Other Japanese automakers might have suffered production curtailments. Japanese auto executives said that their North American plants had not been affected, but they could not rule out interruptions in the future. “There’s no immediate impact. However, we’re investigating,? said Victor Vanov, a spokesman for Toyota’s U.S. manufacturing headquarters in Erlanger, Ky.

Although the Texas pickup plant of Toyota is still running, most of its assembly plants have been idled this week in preparation for the scheduled summer shutdown. The News also reported that other Japanese automakers like the Honda Motor Co. and the Nissan Motor Co. said that their plants in the United States were not affected at this point. Honda is assessing the impact of the damage at Riken’s facilities, which supply its Japanese plants but do not ship parts to its North American plants, said David Iida, a Detroit-based spokesman for Honda.

The said automakers assemble most of the vehicles they sell in the U.S. in North America. But they are banking on engine and transmission shipments from Japan. Toyota, for one, produces 1.6 million product lines annually in North America. The figure represents two-thirds of its American sales of 2.5 million in the previous year. But the automaker is producing 1.4 million engines and only 600,000 transmissions a year in North America. The rest are imported from Japan.

Meanwhile, Nissan, Mitsubishi Motors Corp., Fuji Heavy Industries, Suzuki Motor Corp., Jatco transmission manufacturer and other customers have scaled production in Japan.

Masaki Taketani, an auto analyst at forecasting firm CSM Worldwide in Northville, has this to say: “Most Japanese automakers mentioned shutdowns for two to three days and said they would resume operations Monday.? Japanese automakers have contingency plans to deal with the natural disasters - quakes, tidal waves and typhoons - that strike the country often, he said.

Toyota said that the first shift at its Japanese plants was scheduled to operate normally today but it cancelled production for the rest of the week. “Taking into consideration the situation of the earthquake disaster area and of our suppliers, we have decided that production will not be carried out on all Toyota production lines in Japan for the second shift on Thursday, and for the first and second shifts on Friday,” said Toyota.

The Nissan turn signal is not showing a different plight. Nissan, which purchases transmissions from Jatco, said it was assisting Riken to ensure its supplies. “We are preparing an action plan to minimize any potential impact to our vehicle production,” the company said.