A commission employee used a letter-opening machine the wrong way on Saturday night when processing 2338 postal votes for the Southern electorate of Denison, severing the ballot papers in the middle of the Liberal Party's column.   

While most were repaired and could still be counted, 163 were unreadable and will be treated as informal votes.  

The blunder will have no bearing on how many seats each party will win, as the discounted votes would mostly favour the Liberal candidates who are out of contention.

However, there is a tight race between four Labor candidates for the fifth spot, which will be determined on preferences. 

ALP state secretary John Dowling said there was a very small chance that the error would affect the outcome. 

``If there's a difference of 160 votes between one of the ALP candidates, then that would be concerning,'' Mr Dowling said. 

He said he would need to seek advice about how to handle that situation. 

The error comes as Western Australia prepares to go back to the polls after the Australian Electoral Commission lost 1370 ballot papers in the aftermath of the September federal election. 

Liberal Party Tasmanian director Sam McQuestin said the Tasmanian Electoral Commission had a difficult job. 

``It's disappointing that any Liberal votes are lost,'' Mr McQuestin said. 

Election analyst Kevin Bonham said it was highly unusual and hoped it would be a one-off. 

``The TEC has extremely high standards,''  Dr Bonham  said.

Dr Bonham said there was only a slim chance that the small number of votes lost would affect the outcome.  ``It's possible to imagine a case in which it would, though,'' he said.

Electoral Commissioner Julian Type confirmed the incident.

``As Electoral Commissioner I bear ultimate responsibility for this extensive procedural failure, and I apologise unreservedly to Denison candidates and voters,'' Mr  Type said.