Emergency services' readiness to battle bushfires and respond to natural disasters has been called into question, while Victorians brace for more dangerous conditions ahead.

A damning Auditor-General's report has warned that the Country Fire Authority and the State Emergency Service are "overestimating" the number of volunteers available to be deployed in emergency situations.

The two agencies, which mainly rely on volunteers, lack a "sound understanding" of their volunteer workforces.

"CFA does not know how many volunteers it needs, and SES does not accurately know how many it has," Auditor-General John Doyle said.

"Neither agency can be assured that it has the capacity to respond to incidents when they occur."

The CFA has more than 57,000 volunteers statewide, while the SES believes it has around 5000.

Mr Doyle said the agencies' "decentralised" approaches to recruiting, training, developing and retaining volunteers meant they could not be assured workplace needs were being met.

The audit also criticised ad-hoc recruitment and retention strategies, weak processes to identify skills gaps, and weak deployment processes that could undermine critical incident response.

"Addressing these needs is critical to the long-term sustainability of these emergency agencies," it said.

The audit, which was tabled in state parliament on Wednesday, said the CFA was in the process of addressing its problems, but called the response from the SES "inadequate".

It recommended both agencies improve their oversight and develop strategies to accurately determine where volunteers could be deployed.

CFA chief executive Mick Bourke welcomed and accepted the recommendations of the audit, which came as Victorians prepare to mark the 5-year anniversary of the 2009 bushfire crisis.

"And we know that today, just like on that day, Victoria's emergency services personnel are doing an outstanding job in protecting our communities."

He said the audit clarified and reinforced CFA's current approach to support volunteers, and the CFA would action other recommendations to further strengthen its volunteer workforce.

SES acting chief executive John Casey said an action plan was being developed to implement all of the report's recommendations, and would be completed by the end of March.

"The issues and challenges identified by the Auditor-General reinforce those identified by SES," he said.

"We are working hard to address them."

SES was collaborating with CFA and other agencies in the sector to improve volunteer capacity and capability, Mr Casey said.