A poll shows Labor's core support base is evaporating just five days out from the Victorian election, with Ted Baillieu gaining ground.

The Herald Sun says the private Galaxy poll shows Premier John Brumby will cling onto power, but only with Greens preferences.

The poll shows a collapse in Labor's primary vote, putting at least 18 government-held seats in jeopardy.

On a two-party preferred basis Labor is leading 51-49 but the poll shows the opposition leader has not only secured his own supporter base but is eating into Labor's support in key outer suburbs and regional centres.

The Coalition needs to win 13 seats to govern in its own right, requiring a swing of 6.7 per cent.

The Galaxy poll of 500 Victorian voters, conducted for the Victorian Association of Forest Industries in the middle of last week, gives the coalition a lead of 42-36 on primary vote.

This puts Mr Baillieu within touching distance of the premier's office.

The poll has Labor's vote going backwards at a rapid rate, with most of its primary vote of 43.1 per cent at the 2006 election leaking to the Greens.

The Greens' primary vote is up from 10 per cent at the last election to 16 per cent last week.

Labor's support down ahead of Vic election