Forty-five people were taken to a hospital complaining of eye irritation Monday morning after a parcel being handled at Tokyo's Nihonbashi Post Office began emitting a pungent-smelling smoke, police said.
The parcel contained three bottles of a type of propionyl chloride used in the manufacture of chemical products, including medicines.
The parcel was addressed to Itochu Techno-Chemical Inc., a Tokyo medical company affiliated with leading trading house Itochu Corp.
Itochu officials said the package was sent from Ningbo in Zhejiang Province, eastern China, by Nanjing-based China Jiangsu International Economic & Technical Cooperation Corp.
Post office officials said a 24-year-old employee found liquid leaking from the 5-kg parcel at around 8:30 a.m. and the white smoke appeared shortly afterward.
The parcel also emitted a slight amount of heat.
About 140 workers sorting parcels in the room at the time were told to evacuate the building as a precaution.
The parcel -- measuring 10 cm high, 20 cm wide and 30 cm deep -- arrived at the Tokyo International Post Office on Saturday and was transported to the Nihonashi Post Office later the same day.
Masahiro Haruki, president of Itochu Techno-Chemical, met the press later Monday and apologized for the incident.
There were no serious injuries.