Turkmenistan's capital Ashgabat has overtaken Hong Kong as the world's most expensive city for foreign workers, a survey showed on Tuesday.

Beirut jumped to third place in the 2021 Mercer survey from 45th a year earlier owing to a "severe and extensive economic depression" resulting from multiple crises, including the country's financial trouble, Covid-19 and a deadly blast in the Lebanese port.

Ashgabat rose from second in the previous survey to the first spot due to "high local inflation", Mercer France global mobility practice leader Jean-Philippe Sarra told AFP.

Turkmenistan is almost wholly dependent on natural gas exports and has struggled to recover from the global energy price slump in 2014 that battered the local manat currency and plunged many citizens into poverty.

Despite the long-running economic crisis, authorities broke ground on a major expansion of Ashgabat in May, with autocrat leader Gurbanguly Berdymukhamedov pledging to turn it into "one of the most prosperous cities in the world".

While Hong Kong, with its notoriously expensive housing, dropped to second place, Tokyo also fell one spot to fourth.

Zurich dropped to fifth and is among three Swiss cities in the top 10 along with Geneva (8) and Bern (10).

Two other Chinese cities are among the most expensive in the world for expatriates: Shanghai climbed one spot to number six while Beijing rose to ninth.

Singapore took seventh place.

US cities fell in this year's ranking mostly because of currency fluctuations, and despite rising inflation, according to Mercer.

New York dropped eight spots but was the most expensive in the country at number 14.

The world's least expensive city for foreign employees is Kyrgyzstan's capital Bishkek at 209, according to the survey.