Auckland came 3rd out of 450 cities assessed by international HR consultancy Mercer.

Auckland has again been ranked the third best city in the world for quality of life, according to an an international survey.

Consultancy giant Mercer's Quality of Living Index has ranked the Super City third out of 450 cities. Austrian capital Vienna was top, and Switzerland's largest city, Zurich, was second. Auckland shared third place with German city Munich.

Wellington came in at 15th place, followed by Melbourne at 16th place. Sydney was Australia's top-ranked city at 10.

​Mercer New Zealand CEO Martin Lewington said the City of Sails remained an attractive place to do business.

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"There are a number of factors which have contributed to companies looking at establishing headquarters or relocating expats to Auckland," he said.

"New Zealand's natural environment and subtropical climate, stable political and social environment, and good medical and health services are the top three contributing factors for Auckland retaining third spot in the global rankings."

This year, Mercer introduced a separate ranking on city sanitation, which analysed cities' waste removal and sewage infrastructure, levels of infectious disease, air pollution, water availability and quality.

Auckland ranked 5th and Wellington 6th in sanitation, with Honolulu taking first place, followed by Helsinki and Ottawa sharing second place.

"With Auckland and Wellington's air and water quality being among the world's cleanest, compared to some other popular expat destinations, it means that New Zealand becomes more attractive for global talent," said Lewington.