Shin-Etsu Chemical, the world's leading maker of silicon wafers, restarted a factory near in Gunma, northwest of Tokyo, but said two other plants near the worst hit quake areas in northeast Japan remain offline.

A spokesman said the company was unable to say when operations at the plants will restart. A portion of the silicon wafers usually fabricated at the closed factories are shipped to chip companies overseas, he confirmed.

In a bid to make up the shortfall the company is trying to boost production elsewhere, particularly of 300-mm wafers.