PM defends LNP Longman candidate

Prime Minister Malcolm Turnbull says Labor should consider the ethics of its own members before casting aspersions on the integrity of the Liberal National Party candidate for Longman.

Mr Turnbull on Saturday visited the Longman electorate, giving his full support to "honest" by-election candidate Trevor Ruthenberg.

Mr Ruthenberg earlier this week apologised to voters after he incorrectly claimed to have a medal for distinguished service in peacekeeping and non-war operations.

The revelation sparked calls from Labor for the prime minister to sack Mr Ruthenberg.

Mr Turnbull said "Big Trev" has his full support, and that Labor's claims smacked of hypocrisy given that Susan Lamb, who is recontesting the seat, was forced to quit parliament over the dual-citizenship saga.

"Really the Labor party should be looking at themselves," he said.

"They had Susan Lamb sitting in the parliament there for months and months and months, getting paid at the taxpayers expense, when they knew she wasn't eligible to sit in the Parliament."

Mr Turnbull, who spent the morning at the Caboolture Sports Football Club, conceded the by-election would be a tough one to win.

"It's a by-election in an opposition-held seat and the last time a government won one of those was about 100 years ago, so Trev's got the odds against him," he said.

"But he's a great candidate, he's a straight shooter, he's as honest as he is big (and) he and he alone can deliver for the people of Longman."