The plant is in Yokkaichi in Mie prefecture, about 180 miles southwest of Tokyo.
Kyodo News, quoting the company, said the blast, which occurred in the afternoon, apparently was set off after hydrogen leaked when maintenance workers were involved in demolishing a heat exchanger.
The plant's activities include making polycrystalline silicon for semiconductors and the manufacture of high purity silane gas.
The BBC quoted emergency officials as saying the incident was quickly brought under control.
Celebrity Families of 2014 [PHOTOS]