Seven people involved in a chemical leak at Fonterra's Clandeboye factory this morning are now at Timaru Hospital.
A hospital spokesperson said the seven patients being treated in the emergency department were all in a stable condition.
A leak in a chlorine line has been identified as causing the emergency at the factory, which is about 25km north of Timaru.
Clandeboye operations manager Steve McKnight said the incident, shortly after 11am, occurred while the dry salt plant was being sanitised.
''We believe we have had a leak in a line, and the plant had been on acid wash at the same time, which is what has produced the fumes coming out through there - the mixing of the two processes.''
McKnight said those affected by the fumes were given first aid on site as well as being put through a decontamination shower.
''They have gone into Timaru Hospital as a precaution.''
McKnight said the fumes irritated the airways.
The dry salt plant and administration area were evacuated initially, and the mozzarella plant was subsequently evacuated on advice from the Fire Service.
Around 30 people, about 10 per cent of the staff on site at the time of the incident, were evacuated.
''The lines have been isolated and flushed. We will be back up and running, I expect, later this evening.''
Fonterra chief executive Theo Spierings was told about the incident as he stepped off the stage at the dairy co-operative's annual meeting in Edendale, Southland.
He appeared shocked and his voice showed his concern as he asked for details from an adviser.
Speaking after the meeting, Spierings said the hypochlorite chemical that leaked was used in the cleaning systems and there were 20 staff working in the area.
The chemical was on the floor, so had not affected their skin, he said.
Five workers inhaled the gas and were given precautionary treatment in hospital, he said.
The leak was discovered by workers who saw hypochlorite coming out of the tanks onto the floor.
''It must have been a leaking valve or pipe,'' he said.
Health and safety measures at the plant were carried out immediately and properly, he said.