By Neil Hughes

Published: 02:55 PM EST (11:55 AM PST)

Apple's increased focus on China is paying off, with revenue from the nation quadrupling last quarter, thanks largely to strong sales and quick adoption of the iPhone and iPad.

Apple executives detailed their company's great success in China during their quarterly conference call on Tuesday. The executive team noted the astounding fact that Apple earned just over $3 billion in China in all of fiscal 2010, but achieved $2.6 billion in the same country in the first quarter alone of fiscal 2011. Apple's performance was up four times year over year, riding high on the strength of iPhone and iPad sales.

"We, several years ago, identified China as our top priority," Apple Chief Operating Officer Tim Cook said of the so-called "BRIC" (Brazil, Russia, India and China) countries on Tuesday. "And we put enormous energy into China. And the results of that have been absolutely staggering."

Cook was later asked about the fact that the iPhone remains only available from carrier China Unicom in that country. Recent rumors have suggested that Apple's new CDMA iPhone 4 could make its way to other carriers around the world, particularly in China.

Of course Cook declined to reveal any information that might give away Apple's future plans, though he did reveal that his company is no longer in any contractual exclusive arrangements for the iPhone in any country. The last such deal, with AT&T, concluded earlier this month, with the announcement of the Verizon iPhone.

"I can guarantee you that we are always looking at opportunities to grow," Cook said. "Of course, in the very short-term, I would also remind you that we're constrained on iPhone 4, and we're working around the clock to get as many of these out to our existing partners as we can."