India's steel magnate Lakshmi Mittal dropped out of the top 20 for the first time since 2004, Forbes said, after shares of his main business, ArcelorMittal, plunged, leaving him $10.4 billion poorer with just $20.7 billion.

Mexico telecoms czar Carlos Slim topped the Forbes annual world's richest list Wednesday, holding the edge over Microsoft's Bill Gates who continued to give away billions of his fortune to charity.

Despite a $6 billion hit to his wealth from slumping stock markets over the past year, Forbes said Slim's $69 billion was enough to keep him on top of its global billionaires list for the third straight year.

Gates, the co-founder of Microsoft, had a fortune worth $61 billion, still hefty after having given away $28 billion over recent years to global causes such as fighting AIDs and polio.

The two topped a list of 1,226 billionaires Forbes counted around the world, dominated as ever by Americans -- 425 in total and 11 of the top 20 -- but also underpinned by the rise of concentrated wealth in China and Russia.

Showing the impact of sluggish world growth over the past two years, the list only expanded by 16 this year, and the average billionaire's money pot was unchanged at $3.7 billion.

The number of Chinese billionaires shrank with Asian stock markets, to 95 from 115 last year.

But Chinese and Russian billionaires together still made up 16 percent of the world's total, underpinning the monumental shift in wealth from many of the older industrial powers over the past two decades.

The downturn in the European economy was also evident in the numbers: for the second year running, there were more billionaires in the Asia-Pacific region (315) than in Europe (310).

In the overall list, holding the third spot behind Gates was, as in previous years, US investment guru Warren Buffett, worth $44 billion.

He was followed by France's luxury king Bernard Arnault, with $41 billion, and a newcomer to the top five, Spain's Amancio Ortega, the owner of the Zara fashion chain.

Ortega's net worth surged by $6.5 billion over the past year to $37.5 billion despite Spain's financial straits, Forbes said.

Filling out the top 10 were Larry Ellison of US software giant Oracle, Brazilian mining tycoon Eike Batista, H&M owner Stefan Persson of Sweden, Hong Kong investor Li Ka-shing and Germany's Karl Albrecht, the super-secretive tycoon who owns the Aldi Sud supermarket chain.

In terms of single countries, Russia was second to the United States with 96 billionaires, led by Alisher Usmanov, number 28 overall with $18.1 billion. Usmanov topped the Russian list for the first time based on his control of iron ore and steel producer Metalloinvest.

Forbes predicted his fortune would likely jump over the next year due to canny investments in social media: he has stakes in Facebook, soon to go public, as well as in Zynga and Groupon.

China's billionaires list is led by an Internet tycoon, Robin Li. The chief executive of the country's huge web service and search firm Baidu has earned himself a $10.2 billion fortune.

Behind them were 55 Germans, 48 Indians, 37 British, 37 from Hong Kong, 36 Brazilians, 25 in Canada, and 24 billionaires each from Taiwan and Japan.

In an interview Slim, 72, who controls the regionwide America Movil cellular network, denied his fortune arose mainly from monopolistic power in telecoms networks.

"That's what competitors say, but if that were true, they would take the market from us," he told Forbes.

"The customers are not fools."