New Zealand was on Wednesday named the world's least corrupt nation out of a list of 180 countries, unseating Denmark after a year in which the global recession and ongoing conflicts proved challenging.

The annual index by Transparency International ranked 180 countries on a scale of zero to 10 according to 13 independent surveys, with zero being perceived as highly corrupt and 10 as having low levels of corruption.

New Zealand topped the table with a score of 9.4 after coming second last year. In second place was last year's leader, Denmark with 9.3 followed by Singapore and Sweden tying at 9.2 and Switzerland at 9.0.

Countries at the bottom of the table were those which are unstable or impacted by war and ongoing conflicts that have affected the public sector and torn apart governance infrastructure.

Somalia had a score of 1.1, Afghanistan was 1.3, Myanmar ranked 1.4 and Sudan tied with Iraq at 1.5.

Stemming corruption requires strong oversight by parliaments, a well-performing judiciary, independent and properly resourced audit and anti-corruption agencies, vigorous law enforcement, transparency in public budgets, revenue and aid flows, as well as space for independent media and a vibrant civil society, said Huguette Labelle, chairwoman of Transparency International.

The international community must find efficient ways to help war-torn countries to develop and sustain their own institutions.

Rounding out the top 10 least corrupt nations were Finland, the Netherlands, Australia, Canada and Iceland.

Britain came 17th in the list and the United States was 19th with a score of 7.5.

More than 130 of the countries scored below 5.