In a letter to investors, Mr Cook said that slower growth in China was largely responsible for the shortfall, pointing to an escalating trade war with the US. Apple has also recently signaled that its iPhone business may be struggling by launching special promotions for buying new iPhones-an extremely rare move by the company.
Apple has already turned to several damage-control measures due to lower iPhone sales, including adjusted production at its main suppliers.
The sell-off also affected luxury brands including UK-based Burberry - down 6% - as Apple said China's economic woes and trade war with the U.S. was weighing on consumers in the world's second biggest economy. That led Apple to aggressively market the iPhone XR on its website for $449, about $300 less than its official sticker price.
Apple's stock price hovered around the $143-$144 mark in the first few minutes of trading, down about 9% from Wednesday's closing price of $157.92.More news: ISIS attack in Syria leaves 2 British soldiers seriously injured, report says
"As the climate of mounting uncertainty weighed on financial markets, the effects appeared to reach consumers as well, with traffic to our retail stores and our channel partners in China declining as the quarter progressed", Cook said. "It will be interesting to see how Apple shares react if there's a China trade agreement".
"When asked about the tech giant's shock announcement that revenue for the holiday quarter came in lower than expected, Trump pointed to Apple's stock price increase since the 2016 election as evidence that the company is doing just fine".
He noted that China's economy started to weaken in second-half 2018. Apple originally forecast revenue of between $89 billion and $93 billion.
Despite these challenges, Cook said, "we believe that our business in China has a bright future".
Cook said other factors will also pull down Apple's revenue, including the timing of its iPhone launches a year ago and a strong dollar that means lower revenues when converted to United States currency. Investors worry that the economic slowdown in China and fewer Apple device sales signal the start of a bull market in the U.S. markets.More news: Awkwafina joins ‘Jumanji’ sequel cast
Later in the missive, however, Steve Jobs former right-hand man would admit that the iPhone has also fallen short of expectations, both in its emerging and established markets around the world.
"Apple makes their product in China". Apple shares tumbled after Thursday's open.
In what looks to be an attempt to soften the blow, Cook noted that Apple's services division, which includes apps and music sales, grew its revenue in the December period by 25 percent, to $10.8 billion.More news: Why Rory McIlroy will play more in the USA in 2019