Sydney has slipped out of The Economist's list of the world's 10 most liveable cities "owing to a heightened perceived threat of terrorism".

Australia's largest city was rated 11th in the 2016 Global Liveability Ranking, released on Thursday by The Economist Intelligence Unit, down four places from last year.

Sydney is no longer considered one of the 10 most liveable cities in a list put out by The Economist .

Melbourne topped the list for the sixth year in a row, with Adelaide (5th) and Perth (7th) also making the top 10. The ranking compares living conditions in 140 countries in five categories: stability, healthcare, culture and environment, education, and infrastructure.

"This has been a year undoubtedly marked by terrorism," a summary of the ranking said.