Authorities are investigating a gas leak at a salmon processing plant in southern Tasmania that resulted in 20 people being taken to hospital.

Tassal’s Strathblane facility near Dover was evacuated about 11.30am on Sunday.

Twenty people were taken to the Royal Hobart Hospital for assessment, with six remaining overnight in a stable condition.

An initial assessment by the Tasmania Fire Service indicated carbon monoxide from the operation of forklifts inside the building was likely to blame.

WorkSafe Tasmania is investigating the incident.

Australian Workers Union representative Robert Flanagan said it appeared the forklift being used was not fit for purpose.

“We don’t understand how that could’ve happened,” he told ABC radio.

“We have been in discussions with the company [on Sunday] afternoon regarding the matter, through into the evening.”

Tassal said investigations by the company were underway.

“We have been given clearance from the authorities to recommence operations,” a spokesman said.

The Strathblane plant is Tassal’s original processing facility and has been operating since 1986.