A new poll along with inside information shows the Victorian Liberals are starting to take the rising threat of One Nation very seriously.

So much so, that two inside sources from the Liberals told The Age the party would preference One Nation ahead of Labor at the state's next election in November.

However, the move has been condemned by former Labor premier Steve Bracks who warned the centre-right would be pushed out.

'All that will do is legitimise One Nation and that is outrageous,' he told the Sorrento Writers' Festival last week. 

'It will be the beginning of the end of the centre-right party in this country.' 

A Resolve Political Monitor poll for the outlet suggested Bracks' warning is falling on deaf ears with votes amid the growing popularity of Pauline Hanson's party.

Support for One Nation was present in one in five voters and it appeared to have established itself as a 'third party' alternative for the Victorian election on November 28, rather than being lumped with other minor parties.

Twin surveys in March and April found 21 per cent of the primary vote went to One Nation, compared to 27 per cent for Labor and 29 per cent for the Coalition.

The news follows a wave of success for One Nation in the South Australian election earlier this year where it claimed four seats, including the key gain of Narungga.

Resolve founder Jim Reed said the results indicate Australians are tired of the two-party system.

'One Nation voters are fed up with Labor and don't like Jacinta Allan but think the Liberal Party is not in a position to win or govern either,' he said.

'For some people, backing One Nation is a tactical choice to vote out Labor. For others, it is a Trumpian 'drain the swamp' mentality that seeks to get rid of both major parties. Either way, people are voting for change.

'...This doesn't mean that One Nation are going to suddenly form government, but they are making that mountain harder to climb for the Coalition and may help to keep Labor in power.'