Commission investigating Qld double voters

Queensland's electoral watchdog is investigating more than 600 voters who appear to have cast more than one ballot at the 2015 state election.

The Electoral Commission Queensland has sent please explain letters to 604 residents who may have voted more than once, News Corp Australia reports.

But the commission said the "overwhelming majority" of apparent cases of double voting could be explained by an administrative oversight.

It could not say how many confirmed cases had been identified because the investigation was ongoing.

The investigation comes after the Palaszczuk government last week overturned legislation that required voters to show identification at polling booths.

The laws - introduced by the Newman government - were linked to controversial changes to the declaration rules for political donations, which raised the threshold from $1,000 to $12,800.