A fire broke out about 2 p.m. after an abnormal chemical reaction at Nippon Shokubai Co.'s plant in Himeji, the Japan Times said.
The first explosion occurred about 2:40 p.m. as firefighters were spraying an acrylic acid tank with water, and the second followed shortly afterward, the Times said, citing Nippon Shokubai. The blasts set ablaze a fire engine
A 28-year-old firefighter was killed and at least 30 people were reported injured.
Nippon Shokubai is one of the world's biggest makers of acrylic acid, the main ingredient of a resin called SAP, which is used in diapers.
The plant produces about 20 percent of the world's SAP and 10 percent of global output of acrylic acid.
Operations at the plant are likely to be halted for a long time and other makers of SAP resins are operating on a full-production footing, leaving little room for back-up production, the Nikkei business daily said on Sunday.