Police raided the headquarters of Japan's largest yakuza syndicate, the Yamaguchi-gumi, on Tuesday after 14 workers at a waste disposal plant in Kobe became sick.

The police said the incident was attributable to toxic gas in waste that was taken to the dump by a local firm that had a contract with the gang.

The police said the gas was hydrofluoric acid, a liquid poison, and that it leaked from a plastic tank that was damaged en route to the plant.

The plant is not permitted to dispose of the chemical.

On Aug. 3, the workers complained of nausea and eye pain after inhaling the gas at the plant, which is located on Rokko Island in Kobe, although their condition was not serious.