The 4.7-inch iPhone 6 and 5.5-inch iPhone 6 Plus will support more than 200 telecoms carriers worldwide, including all three in China - a key growth market for the company.
Apple is expected to introduce its first new product since the iPad in 2010, a smartwatch, later on Tuesday.
Bernstein Research analyst Toni Sacconaghi estimated on Tuesday that if Apple were to sell 30 million iWatches at $250 each, it would add about $7.5 billion to its revenue.
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