THE NATIONALS' primary support has slumped to just 2 per cent of Victorian voters, according to a Newspoll survey.

That's down from 6.8 per cent at the 2010 election.

The poll shows Labor has an election-winning lead for the first time since the election.

The voting intentions survey shows Labor has 55 per cent of the two-party preferred vote compared with the Coalition's 45 per cent, representing a six-point surge in the ALP's primary vote since a poll in July-August.

But the poll's methodology was criticised by Monash University political scientist Dr Nick Economou, who said the results were not a reflection of the Nationals' popularity.

"This is a failing in the polling system, a statistical problem with random polling," he said.

"When I saw these results I thought, 'They have to be wrong', and I think they are."

Because Victoria has a huge metropolitan population, compared with rural and regional areas, random sampling tended to under-represent country voters, Dr Economou said.

"The Nationals' vote tends to be very stable and they have been doing very well in Victoria for a while," he said.

"This poll does not correspond with how the National party performs at elections."

Dr Economou said the overall performance of the Government under Premier Ted Baillieu was not as bad as the poll indicated.

Newspoll director Martin O'Shannessy told The Weekly Times smaller parties such as the Nationals did poll poorly on primary votes in between elections.

"It can be a dynamic of how polling works," he said.

Smaller parties tended to be generally less visible out of campaign mode, he said.

"They are like the wire between two telegraph poles ... coming up to an election they will tend to poll better," he said.

Planning Minister Matthew Guy said last week that past governments had mid-term blues in their first term, including the Carr Labor government in NSW, the Kennett coalition government in Victoria, and the Howard federal government.