This is the third year in a row New Zealand has been named the least corrupt country by the index.

New Zealand has once again been rated the least corrupt country but Open Government Minister Clare Curran warns there's still more work to be done.

On Thursday, Transparency International released its latest Corruption Perceptions Index. New Zealand took out the top spot, ahead of 179 countries.

This is the third year in a row New Zealand has been named the least corrupt country by the index.

TRANSPARENCY INTERNATIONAL NZ has once again been ranked the least country in the world.

While New Zealand was ranked in the top spot, its score has dropped compared to previous years. It received a rating of 89 out of 100, down from 90 in 2016, and 91 in the previous three years.

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In 2016, Denmark tied with New Zealand for the top spot, it has now dropped slightly behind to the second least corrupt country in the world, with a rating of 88.

Australia ranked 13, with a score of 77 out of 100. Canada and the UK ranked eighth equal.

Curran said the public sector continued to show "the high standards of conduct and integrity", when compared to other countries around the world.

"While we continue to hold the position of least corrupt country, and already have high standards of conduct and integrity, we must not be complacent," she said.

"These results show we are not immune to behaviour and actions that can erode the great work done by the majority of people in the public sector.

"Our focus must be on building and maintaining the public's trust in the integrity of the public sector, a key enabler in our ability to do better for New Zealand and New Zealanders."

Curran said the Labour-led government was also committed to reviewing and improving access to information, and had started work on human rights in the digital environment.

"Our commitment to open government plays an important role in New Zealand's democratic system, underpinning the public's respect, trust, and confidence in the integrity of government."

These, and previous results, showed countries that ranked as the least corrupt generally had higher levels of media freedom, greater access to official information (particularly on public expenditure), and higher standards of conduct and integrity for public officials, Curran said.