The Liberal Party will open nominations on Wednesday, with the pre-selection ballots for both electorates to be held in late September. 

The Labor Party on Monday night revealed it would field a candidate.

 The party’s candidate for the 2014 election, Roy Reekie, said he was keen to go again. 

“It’s not unexpected and I knew it would be about this time of year,” Mr Reekie said.

“This is an opportunity to break the political mould, this doesn’t have to be a blue ribbon seat. It’s a chance to vote for someone else. 

“Denis has been a good local member, but this is a chance to have a new, effective voice for our region in the parliament.”

A spokeswoman for the National Party said a decision was yet to be made, but running candidates was “a likely scenario”. 

Victorian Greens leader Greg Barber says his party will run candidates for the South West Coast and Polwarth by-elections.

"This is a chance for locals to have their voice heard. As long term Liberal seats, both Labor and Liberal have neglected the area,” he said.

"The threat of gas drilling has the community up in arms. Labor, Liberal and the Nationals don't have a policy you can trust.”

The Australian Country Party said it would consider running candidates.