Tokyo has officially become the world's most expensive city for expatriates, overtaking the Angolan capital of Luanda, while Osaka has moved up to third place, according to a global survey by consulting firm Mercer LLC.

After Osaka, Singapore at 6 and Hong Kong at 9 were judged the costliest cities in Asia, while Chinese metropolises, including Shanghai, Beijing, Shenzhen and Guangzhou, rose on higher prices for goods and the stronger yuan, according to Mercer's 2012 Cost of Living Survey.

"Recent world events, including economic and political upheavals, have affected the rankings for many regions through currency fluctuations, inflation and volatility in accommodation prices," Mercer said Tuesday while unveiling the findings.