A release of built up gas from the Longford Sewage Treatment Plants will occur. 

The works will be completed by a crane, a spokesman said. 

"TasWater apologises should the gas release result in further odour, but assure residents it is necessary as part of the treatment process and particularly to protect the safety of our staff and the lagoon cover," the spokesman said. 

"The release is regrettably unavoidable, likely due to an increased level of high-strength waste."

The lagoon cover is an "essential" part in limiting the odour to the town. 

TasWater said the release is not a common event. 

"TasWater is investigating the cause and impact of odours in the town and asks residents who may notice an increase in odour during the release to please contact our customer service centre on 136992," the spokesman said.

"Information on the strength of odour and where it is noticed will provide valuable information as our investigation continues."