With 14 billionaires, Dubai is home to the highest concentration of billionaires in the Middle East. It ranks 18th globally out of the ranking of the 25 most billionaire-heavy countries, compiled by intelligence firm WealthInsight.

In the last five years, the average per-capita wealth of billionaires living in the UAE has dropped by a tenth, though the number of billionaires has doubled, according to London-based WealthInsight, which surveyed 1,340 billionaires.

"As expected, the UAE has a number of foreign national billionaires in the country, coming from countries including Bahrain, India, New Zealand, Pakistan and Saudi Arabia," said Stephen Gross, a senior analyst at WealthInsight, in the report.

But he added that Dubai's position might be "undermined" by Singapore, which jumped to 19th spot to become the UAE’s biggest competitor.

"In terms of competition with Dubai, it has more to do with the Indian business," said Gross, cited by Dubai daily The National. "There's a lot of Indians who are not residents in India, and those are the ones that Dubai and Singapore are both competing for."

Both Dubai and Singapore are seen as a haven for billionaires seeking refuge from hefty tax bills, particularly as scrutiny on private banking accounts in Switzerland heats up. Singapore is expected to benefit from the influx of billionaires from China, which has five cities in the top 25, including Shanghai in 8th spot.

The Top 25 cities by number of billionaires (Source: WealthInsight’s HNWI Database):

1.New York

2. Moscow

3. London

4. Hong Kong

5. Mumbai

6. Istanbul

7. San Francisco

8. Shanghai

9. Paris

10. Beijing

11. Chicago

12. Shenzhen

13. Los Angeles

14. Houston

15. Dallas – Fort Worth

16. Tokyo

17. Guangzhou

18. Dubai

19. Singapore

20. Jeddah

21. Sao Paulo

22. Taipei

23. Amsterdam

24. Riyadh

25. Hangzhou