Victorian authorities are looking into claims of corruption in the state’s Liberal Party.

In what has been described as “a bombshell inquiry that threatens the Napthine government’s hold on power”, reports say the Victorian Ombudsman has interviewed Liberal candidates in two Labor-held seats in southeast Melbourne.

The councillors were questioned over planning decisions made in the City of Casey, one of Victoria’s biggest municipalities.

It is the same area that the Coalition declared “ground zero” for its re-election bid in the upcoming state election.

News Corp media outlets are reporting that Geoff Ablett; Liberal candid­ate for Cranbourne, and Amanda Stapledon; Liberal candidate for nearby Narre Warren North, have been interviewed by the Ombudsman.

Both have denied any wrongdoing.

Rumours have been circulating about questionable donations, with further allegations raising questions over the role of “key members” of the business community.

The Victorian LNP is claiming that the “serious and potentially defamatory allegations’’ are just a smear campaign meant to scuttle their ship on the eve of the election.

New Corp says anti-corruption investigators have seen information relating to specific council decisions and political donations, which was also made available to the Liberal hierarchy months ago.

If the claims published in media outlets do hold weight, they could have the potential to deal serious damage to the Victorian LNP.

Links have been drawn between these claims and coverage of Liberal Party Victorian director Damien Mantach, who was secretly recorded earlier this year telling branch members what to do about donation concerns.

Reports surfaced in August that Victorian LNP Premier Denis Napthine used his position as Racing Minister to promote and attend a Liberal Party fundraiser for Ms Stapledon, which also involved the part owners of champion racehorse Black Caviar, triggering allegations of a conflict of interest.

Currently, the ­Coalition holds 44 seats in State Parliament, Labor has 43 seats and one belongs to independent MP Geoff Shaw.

The most recent Newspoll put Labor ahead of the Coalition - 54 per cent to 46 per cent, two party-preferred.