Road crews closed most of a left-hand lane in an eastbound overtaking section on the Princes Highway near Illowa on Friday.

Speed limits have now lowered to 60 km/h due to the hazard.

Regional Roads Victoria south-west director Vanessa Schernickau said the lane may remain closed for some days.

"Now weather has improved, our crews are on the ground working as quickly as possible to repair potholes and reopen the lane in the coming days," she said.

"We thank everyone for their patience over the weekend."

The federal government in early 2019 flagged the highway between Warrnambool and Port Fairy for upgrades worth $60 million, but it now blames the state government for not starting that work.

South West Coast state opposition MP Roma Britnell said the road was "literally at breaking point".

Ms Britnell called on the state government to match the federal funding in the upcoming state budget.

Her office has received "dozens" of complaints about the new potholes since late last week.

She said the event was "not a one-off" but road closures showed the situation had become "desperate".

Princes Highway West Action Alliance spokesman Stephen Lucas agreed the strip was not the only place the road was failing.

"Heavy rain events like we have just had exacerbate the problem and point to the need for long-term funding for rehabilitation," Mr Lucas said.

He said the alliance was currently trying to determine why a memorandum of understanding for the $60 million had not been signed between the state and federal governments.

"The agreement to forward funds to the state, who does the work, has to be signed off by both the state and federal governments, and that hasn't happened," Mr Lucas said.

"The holdup could be on either side ... irrespective there needs to be agreement and the work can begin."

It's understood Victoria's Transport Department still needs to identify and plan improvements on the road to address specific issues and it is working with its federal counterpart as needed.

Mr Lucas, who also owns Warrnambool Bus Lines, said transport businesses had learned to live with the road conditions.

"We are used to having pavement failures, while it is a safety concern, it is only a concern until the offending area is repaired. Regional Roads get onto those repairs quickly."

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