Australia has once again slipped in a global corruption index, suggesting Federal Government measures to crack down on bribery and the diversion of public funds are failing.

Snapshot of corruption index: 1. New Zealand 2. Denmark 3. Finland 3. Norway 3. Switzerland 13. Australia 175. Yemen 177. Afghanistan 178. Syria 179. South Sudan 180. Somalia

In a corruption perceptions study of 180 countries conducted by Transparency International, Australia ranked as the 13th least-corrupt nation, ahead of Hong Kong, while New Zealand won top ranking as the cleanest.

But in a disturbing trend, the index showed Australia's corruption score had slipped eight points over the past six years, a trend which was described as a "notable decrease".

Australia scored 85 out of 100 in 2012, and 77 out of 100 in 2017.

The lower the score, the higher the perception of corruption.

Transparency International Australia chief executive Serena Lillywhite said developed countries — including Australia — appeared to be lagging in their efforts to combat corruption in the public sector.

Ms Lillywhite cited a range of perception issues currently in the political and public sector spotlight in Australia that are damaging the nation's push to be seen as a democracy where corruption is targeted and weeded out.

"The misuse of travel allowances, inadequate regulation of foreign political donations, conflicts of interest in planning approvals, revolving doors and a culture of mateship, inappropriate industry lobbying in large-scale projects such as mining, and the misuse of power by leading politicians have no doubt had an impact," Ms Lillywhite said.

Calls for federal anti-corruption watchdog

Concern about Australia's ranking comes as debate continues about the need for a federal anti-corruption watchdog similar to the Independent Commission Against Corruption (ICAC) in NSW.

Australia's mining dominance in Africa is a particular concern, given 140 ASX-listed companies have operations in 34 countries across the continent.

"This should have alarm bells ringing for Australian miners. It underscores the importance of our work to combat corruption in mining approvals," Ms Lillywhite said.

Transparency International Australia chairman Anthony Whealy QC said Australia's ranking suggested a failure to deal with serious public sector issues.

"These include money laundering, whistleblowing, political donations and the effectiveness of our systems," Mr Whealy said.

"The Government has simply not faced up to the need to have an independent corruption agency at a national level."

'More than 6 billion people living in corrupt countries'

The annual index examines 180 countries for perceived levels of public sector corruption.

Business leaders and sector experts were interviewed about the success of measures to prevent corruption, and government efforts to enhance integrity and legal protections for whistleblowers, journalists and corruption investigators.

While New Zealand, Denmark, Finland, Norway and Switzerland were the top five least corrupt nations, countries perceived to be the worst were Somalia, South Sudan, Syria, Afghanistan and Yemen.

With more than two-thirds of countries ranking poorly, the survey concluded that more than 6 billion people live in countries that are corrupt.

It highlighted the relationship between corruption and freedom of expression, which is seen as "vital for exposing corruption and the injustices that it causes".

Transparency International said most countries failed to protect the media, which plays a critical role in preventing corruption.