Apple warns iPhone sales may take a big hit

Apple warned investors its holiday iPhone sales may be "lower than anticipated."

The company cited sluggish sales in China as the country wages an ongoing trade war with the United States.

"While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China," Apple CEO Tim Cook wrote in an investor letter, pointing to "rising trade tensions" with the United States.

Apple is forecasting revenue of $84 billion for the holiday quarter, down from an earlier estimate of $89 billion to $93 billion.

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