Salmon farming company Tassal is investigating the cause of a fire at one its processing plants in Tasmania's south.
Workers were on Tuesday alerted to some smouldering on an empty fish pen in Nubeena, southeast of Hobart, a Tassal spokesperson said.
The smouldering at the company's Storm Bay Zone was controlled and extinguished immediately, the spokesperson confirmed.
The company believes it started as a result of a process to brand equipment.
"Tassal is conducting an investigation on the cause to prevent re-occurrence," the Tassal spokesperson told AAP in a statement.