Investigators have found there is no ammonia gas leak at Mataura's old paper mill, where toxic ouvea premix is stored, following an incident this afternoon.
Fire and Emergency told 1 NEWS the sprinkler system at the paper mill was activated by the frost, which was thought to have put the premix in contact with water.
The premix, a by-product of the Tiwai Point aluminum smelter, lets off ammonia gas when wet.
Two fire trucks from Mataura and a command unit from Invercargill were called to the scene just after midday today.
Investigators went in to conduct gas readings and found no ammonia gas leak.
The road surrounding the building was closed for some time but has since reopened.