The Department of Labour is investigating the cause of a chemical spill at a Whanganui tanning factory that has left two men in serious condition in hospital.
Factory staff and emergency workers were affected by hydrogen sulphide gas from the chemical spill which occurred at Tasman Tanning in Castlecliff just before 5pm on Friday.
Twenty-one people were taken to Whanganui Hospital. Those treated were factory workers, a fire officer and five ambulance crew members.
Two critically ill men, in their early 50s, were flown to Wellington Hospital and by Saturday they had improved to a serious but stable condition.
Radio New Zealand News understands one of the men is breathing on his own.
The remaining 19 people have since been discharged.
Other staff at the factory, which employs 200 people, will be monitored for any reaction to the gas.
Department of Labour investigators began their investigation at the Tod Street plant on Saturday. A department spokesperson said the inquiry could take six months.