China has passed the U.S. to become the global leader in new iOS and Android activations. China has been the world’s largest mobile phone market for some time, now it appears to have become the top smartphone market as well.

According to a recent study published by Flurry, China’s rate of device activation has surged in the last year. In January of 2011, China accounted for just 8% of worldwide Android and iOS activations. By the end of 2011 that number had climbed to 17%. In just three months, the number has climbed again. China passed the U.S. in February as Chinese activations reached 23% and U.S. activations fell to 22%. As of March (with the data projected through the end of the month) China accounts for 24% of iOS and Android activations worldwide, while the U.S. accounts for 21%.

China also had the fastest growth (by far) in terms of app sessions (the launch and use of a smartphone application). Numerous countries around the world showed remarkable growth in the number of app sessions. In Turkey, Thailand, and Saudi Arabia, for example, app sessions grew by nearly 400%. In Russia they grew by just over 500%, while in Argentina they grew by nearly 600%. In China, however, app sessions grew by a staggering 1126% between the first quarter of 2011 and the first quarter of 2012.

Finally, the study looked at the worldwide distribution of iOS and Android app sessions. While the U.S. held the overall top spot in app sessions (which indicate the largest installed user base), its lead has shrunk in the last twelve months. In the first quarter of 2011, the U.S. accounted for 56% of worldwide app sessions. The rest of the top ten countries combined to account for 27%, and the rest of the world combined for 17%. In the first quarter of 2012 (again projecting the last ten days of the quarter), the U.S. accounts for 10% fewer app sessions, while the rest of the top ten and the rest of the world account for 3% and 7% more, respectively.

Given China’s massive growth as a smartphone market in the last twelve months, the efforts of smartphone makers like Apple to increase their presence in that country make a great deal of sense. Last month Apple reached an agreement to begin offering the iPhone on the second of China’s three major carriers, China Telecom. The move was partly aimed at alleviating Apple’s losses in market share in China.

The full study can be found on Flurry’s blog.