SINGAPORE - Singapore has climbed one rung from fifth place last year to become the fourth most expensive city in the world for expatriates, according to a report by research firm Mercer.

Singapore is also the second-priciest city in the Asia Pacific region, beaten only by Hong Kong, Mercer found in its annual cost of living survey.

The most expensive city for expatriates was Luanda in Angola, which is in southern Africa, for the second year in a row.

That was followed by N'Djamena in Chad, which is a landlocked country in central Africa. Hong Kong came in third.

"While Luanda and N'Djamena are relatively inexpensive cities, they are quite costly for expatriates since imported goods come at a premium," said Mr Ed Hannibal, partner and global leader for Mercer's mobility practice, in a statement.

"In addition, finding secure living accommodations that meet the standards of expatriates can be challenging and quite costly as well. This is generally why some African cities rank high in our survey."

Mercer said that African, European and Asian cities were generally the most expensive for expatriates due to currency fluctuations and the impact of inflation on goods and services.

Cities in Asia accounted for four out of the 10 most expensive worldwide. Apart from Hong Kong and Singapore, Tokyo and Shanghai also made it to the list.

Tokyo dropped four spots to rank seventh while Shanghai jumped four places to 10th.