At least four men died in an explosion on Thursday at a chemical plant in Osaka in western Japan, the Kyodo News agency said citing local firefighters.

The blast ripped through the plant operated by Morita Chemical Industries Co. shortly before 09:00 local time (midnight GMT) when workers were conducting maintenance work at a unit which produces fluorine-containing substances, including toxic boron trifluoride.

One worker was killed on the spot, while three others were rushed to a hospital but later confirmed dead. In addition, several workers were hospitalized with injuries of various degrees.

The plant's administration said a section of the roof was blown off by the explosion, causing an emission of a small amount of toxic gases in the atmosphere.

The officials said there was no threat to the local population.

Local emergencies services and police have launched a rescue operation at the site of the accident.

MOSCOW, December 24 (RIA Novosti)