Apple on Tuesday proved once again with its quarterly earnings that it's practically minting money selling iPhones. The company posted quarterly revenues of $37.4 billion, up six percent from last year, and a profit of $7.7 billion, up 12 percent from last year.

And there's nowhere in the world that Apple is growing faster than in China.

"It's very, very exciting what we're seeing there," said chief executive Tim Cook on an earnings call Tuesday evening.

China is, by far, the spot where Apple is growing the fastest, bolstered by recent lucrative deals that the company has made with China's largest wireless carriers.

And that's not even where Apple has the biggest revenues--at least not yet. Both the Americas and Europe beat out China in terms of places where the firm pulls in the most sales, meaning that there's in theory a lot of potential in China for Apple to grow.

Apple, of course, faces a lot of competition in China. That comes not only from Samsung phones running Google's Android operating system, but also from local smartphone makers such as Xiomi, Huawei and Lenovo. The key for Apple will be laying the groundwork among customers who will use their devices to pour more money into Apple's apps, music and movies.

So far, Cook seems upbeat about Apple's prospects there. Sales of both the iPhone and iPad were up roughly 50 percent from the same period last year, he said. And the strongest category of growth this past quarter was in the section that contains the App Store.

"That area is almost doubling year-over-year," he said.