The works due for completion in August now won't be completed until mid-to-late 2022, a decision slammed by the opposition.

Liberal South West Coast MP Roma Britnell said it showed "incompetence" on the Labor government's part, but Regional Roads Victoria safe roads director Scott Lawrence said there was no option but to delay.

"We apologise that this important project is taking longer than originally planned and share the community's frustrations as we all want to see these road improvements and safety upgrades completed as quickly as possible," Mr Lawrence said.

He said construction schedules were significantly impacted following the "wettest spring and start to summer in the Warrnambool area in decades".

From September through to the end of December 2020 the Warrnambool area experienced almost 390mm of rainfall - the highest total rainfall over this period in the area in more than 20 years.

Mr Lawrence said it directly impacted excavation and construction on the sections where the road was being widened with several sections having to be reworked due to flood damage to the underlying road structure.

But Ms Britnell said that was a poor excuse that "didn't pass the pub test."

"There aren't many unknowns in this - they knew how much earthmoving would be needed, they know that it rains - I can't understand how a basic project like this can be so delayed," she said.

"First the excuse for the delays was COVID, now it's the weather - the truth is it's poor planning and project management from the Andrews Labor government.

"It's poor planning - plain and simple - and that poor planning is going to cost taxpayers.

"It's just another example of Labor not being able to manage a project - big or small."

Princes Highway, between Panmure and Warrnambool, has been identified as one of Victoria's high-risk regional roads.

In the five years between 2012 and 2017, 12 people suffered serious injuries and tragically two people lost their lives on the stretch of road.

Some progress has been made on the works, including safety barriers on the divided section of the highway between Allansford and Warrnambool and an overtaking lane.

On the undivided section between Allansford and Panmure, road widening, road construction and some sealing works have been completed along the highway between Hopkins Falls Road and Brucknell Creek Bridge.

"We will continue do all we can to minimise the impacts to locals and road users as we keep this project moving forward over winter and into the warmer months," Mr Lawrence said.

"Where it is safe to do so, we are making every effort to enable speed limits to be raised from 60km/h up to 80km/h in certain sections outside of construction hours and will keep the community advised of any traffic changes."

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