More than 20 firefighters are decontaminating a Christchurch corrections facility tonight after two probation officers were affected by a hazardous substance.
Fire and Emergency said four fire engines and a hazardous chemicals unit were called to the Ensors Road Community Corrections site about 4.55pm tonight.
St John's Ambulance says the two officers have been taken to hospital in a moderate condition.
Police said the officers visited two addresses this afternoon and complained of burning throats, rashes and nausea when they returned to the office.
The assistant area commander for fire and emergency services Steve Kennedy said they were yet to determine what caused the symptoms.
"We used a photo-ionisation detector that picks up a wide range of substances.
"It got no reading from clothes or the vehicle.
"We don't actually know what it was that caused the reaction. It affected nobody else - even the other people who they've been in contact with - so it'd be fair to say it's a bit of a mystery to us at the moment."
A spokesperson said 28 other people were in the area at the time but did not need medical attention.