Apple was plunging 8.5% in the first minutes of trading on Thursday after warning that sales in China were slowing.

That fall equates to a drop in market capitalization of around $64 billion.

Global stocks slid after a shock revenue-guidance downgrade from Apple and troubling comments about the economic impact of the US-China trade war from CEO Tim Cook.

Major US indexes lost ground, with the Nasdaq down 1.3%, the Dow Jones off 1.2%, and the S&P 500 losing 0.9%.

After a roller-coaster day of trading to start 2019, global markets were enduring more turbulence Thursday after Apple warned investors that sales were slowing in China, reigniting fears about a slowdown in the world's second-largest economy.

"While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China," Apple said after the close of trading on Wednesday.

Apple plunged 8.5% in the first few minutes after the open at 9.30 a.m. ET (2.30 p.m. GMT).

Apple's shock revenue-guidance downgrade, along with troubling comments from CEO Tim Cook about the economic impact of the US-China trade war, added to fears that had already gripped investors.

"The trade tensions between the United States and China put additional pressure on their economy," Cook said in an interview with CNBC on Wednesday.

Cook's words, as well as continuing fears around monetary-policy tightening from global central banks and a general slowdown in the world economy, have helped push markets downward on the second day of trading in 2019.

Here's the scoreboard:

US stocks dropped sharply Thursday following Cook's comments, which came after markets closed on Wednesday. The tech-heavy Nasdaq was off 1.3%, while both the Dow Jones Industrial Average was 1.1% lower, and the S&P 500 dropped 0.9%.

Thursday following Cook's comments, which came after markets closed on Wednesday. The tech-heavy was off 1.3%, while both the was 1.1% lower, and the dropped 0.9%. In Asia, China's Shenzhen Composite ended 0.8% lower, while Japan's Nikkei 225 lost 0.3%.

ended 0.8% lower, while Japan's lost 0.3%. As European trading kicked off, shares also fell, with the Euro Stoxx 50 broad index down 0.6% and Germany's DAX down 0.8%.

Thursday's market moves extend a brutal start to the new year after 2018 ended on a sour note for markets. The S&P 500 fell 6.2% in 2018, booking its worst year since the financial crisis and worst December since the Great Depression.

Read more: Chinese stocks were the worst on earth in 2018, losing 27% — here's why

Away from stocks, currency markets also took a pounding overnight with a suspected "flash crash" sending the dollar, the pound, and the euro sharply lower and pushing the Japanese yen into orbit.

The moves, which are also thought to be linked to Cook's comments, saw investors pull money rapidly out of Western currencies like the dollar and push it into the perceived safe haven of the yen.

Sharp moves in the yen

At its peak, the yen was up by about 2.5% against the dollar. The dollar tumbled to an intraday low of 104.96 yen, its lowest since March.

The Australian dollar, often considered a gauge of global risk appetite, fell to its lowest level since 2009 in early Asian trade to an intraday low of $0.6776.

The spike in risk aversion triggered massive stop-loss flows from investors who had held short positions on the yen for months. A lack of liquidity, with Japan still on holiday after the New Year, added to the sharp surge.