The head of Victoria's Country Fire Authority (CFA) Russell Rees has announced his resignation, after coming under mounting criticism for the CFA's handling of the Black Saturday bushfires that killed 173 people.

Mr Rees announced he was standing down at a press conference in Melbourne this morning, saying: "I am making the decision to go now so that the future of the CFA is assured."

"Now is the time to change. Now is the time for CFA to look forward."

Mr Rees rejected suggestions he was forced out because of his performance on Black Saturday.

"This decision is mine. I came to the conclusion at the end of the season, consulted with my family, consulted with the CEO, and now is the right time," he said.

Struggling to control his emotions at times, Mr Rees said it was important to stay on after Black Saturday to guide the organisation through a difficult time.

But he is leaving in July, 18 months before the end of his contract, and before the Royal Commission's final report.

"It would be inappropriate of me to stay on, and then leave half way through what I see as being a major change period that will come out of the recommendations of the Commission," he said.

He declined to make any final assessment of his performance on Black Saturday, saying that was up to the commission to decide.

Mr Rees says his legacy will be the work he has done in implementing new management systems and safety systems for firefighters.

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Victorian Premier John Brumby says he understands and supports Mr Rees' decision to quit.

"It opens up new opportunities for the organisation and I think these are the things the very things that Russell would see going forward," he said.

"That new blood can come in, further changes can be made and the organisation can be furthered strengthened in the future."

Emergency Services Commissioner Bruce Esplin praised Mr Rees as a hardworking career fire officer who was a passionate and strong champion for the volunteers of the CFA.

He said he believes Mr Rees considered resigning after the bushfires but decided to stay.

"Perhaps it was harder to remain as chief and carry the organisation through the first year of the Royal Commission and the next summer. And I think he decided that was the hard and appropriate thing to do," he said.

He said Mr Rees is putting the CFA first.

"His advice to me was he wanted to put the organisation first and give it the chance to appoint a new chief fire officer to take it into the future."

Mr Esplin said Mr Rees should be credited with helping the CFA work more closely with the DSE.

But Mr Esplin does not necessarily support a union call for amalgamation.

"Amalgamation is not the only answer to achieving the change and improvements that are necessary. Sometimes you lose more than you gain."

Peter Marshall, from the United Firefighters' Union, has thanked Mr Rees for his service.

"Certainly like all firefighters, he's done the best he could [have] at the time. And no doubt we all have the benefit of hindsight," he said.

The president of the Volunteer Fire Brigades Association, Gary Lewis, has thrown its support behind Mr Rees.

He says Mr Rees' service can not be judged on the events of one day.

"There [are] a lot of things that Russell has done over the years since he's been chief officer [that] have [contributed to] outstanding growth for CFA," he said.

"Chief officer standing orders, management of the operations side of CFA has been really outstanding over the years."