Apple's revenue in China came in at $13.17 billion during the December quarter, a drop of nearly $5 billion from a year ago, when Apple reported $17.96 billion in China revenue. Apple's revenue is typically highest during this quarter, the first of its fiscal year.

Apple saw a similar slowdown between the December 2015 and December 2016 quarters, when China revenue fell 12 percent.

Apple's revenue in China was $11.41 billion during the September quarter, Q4 of its 2018 fiscal year. Revenue was also down slightly from last year in Europe and Japan.

In an interview following the report, CEO Tim Cook told CNBC, "As we got into January, things have improved...from where they ended in December and that gives us some optimism. Of course you don't know what will continue but I would also point out that seems to map to trade tension as well, that there is a bit more optimism in the air in January, or certainly I feel that anyways. I'm encouraged by the comments coming out of both countries."