Prime Minister Tony Abbott has declared the Canning by-election a "real" test of his government.

Mr Abbott contrasted the September 19 poll in the West Australian seat with the latest Newspoll which showed Labor leading the coalition 54-46 per cent on a two-party basis.

The Labor opposition has maintained a lead over the government for the past 16 months.

Labor leader Bill Shorten's 40 per cent rating as preferred prime minister put him five points ahead of Mr Abbott.

Speaking on Thursday Island where he has set up office for a week, Mr Abbott talked down the relevance of the opinion poll.

"The Canning by-election is obviously real in the sense that other indicators aren't," he told reporters.

"We've got a good story to tell."

Mr Shorten told reporters in Brisbane that voters did not need an opinion poll to tell them Mr Abbott was leading "one of the most incompetent governments in the history of federation".

"We've seen the deficit has been doubled, unemployment is up, we see growth down, we see real wages growth down, we see confidence down, we see the NBN (cost) in the two years that this government's been in, has nearly doubled," he said.

Treasurer Joe Hockey said the coalition had been in a similar position before the 2004 election, when John Howard went on to win a majority in the lower and upper houses.

"I saw this in 2004, I saw it in 1998," he said.

"I have seen it previously, where we have gone on to win an election, even weeks and months just after those sort of polls."

Newspoll's David Briggs says there could be a very close result on September 19, taking into account earlier polling which showed a 10 per cent swing against the Liberals in Canning.

"If the stocks of the government, and Tony Abbott in particular, continue to deteriorate it might be a disincentive for the local voters in Canning to vote for the Liberal candidate," he said.

There was potential for the polls to get "a little worse" for the coalition because of voter concerns about Mr Abbott's personal performance.