Emergency services were called to the Tiwai wharf at 2.30am following reports that workers had inhaled pitch fumes while working at the aluminium smelter site.
Some of the workers, comprising seven stevedores, five truck drivers and four New Zealand Aluminium Smelters (NZAS) team members, experienced nausea, coughing or vomiting.
NZAS general manager Ryan Cavanagh said the vessel Rakiura Maru was delivering liquid pitch to the smelter before transporting metal back to Japan.
It is believed the pitch tank system vented while the metal was being loaded on to the ship, releasing pitch fumes into the surrounding wharf area and affecting the working team.
Mr Cavanagh said anyone who came into contact with pitch fumes required decontamination, and the Fire Service responded with two appliances.
Fire Service assistant area manager Julian Tohiariki said decontamination sites were set up at the wharf and at Southland Hospital.
Workers were taken to Southland Hospital as a precaution, and later released and cleared to return to their work.
