The Fire Service says a chemical that killed six pigs and a cat at an Ashburton property could be an organic phosphate used for killing grass grubs.
But it says staff are still not completely sure what it is.
Up to 20 firefighters attended the incident at the Cochranes Road property just outside Ashburton.
Local deputy chief fire officer Graham Baker says what is left of the chemical has been stored safely awaiting disposal.
Earlier the Fire Service finished decontaminating staff and two members of the public at the property.
The Fire Service was notified about at about 8.30am on Saturday that a chemical had been spilt and a number of pigs and a cat were dead.
The substance came from a 45kg box container in an open shed.
It is believed sheep got into the shed and knocked the box over and then the pigs ate the chemical and died.