U.S. stocks slid after Apple (AAPL) lowered its outlook for fiscal first quarter 2019 revenue, validating concerns of deteriorating demand for flagship products from one of the country’s largest tech companies and propelling worries of a global growth slowdown.

The S&P 500 (^GSPC) fell 2.48%, or 62.14 points, as of market close Thursday. The Dow (^DJI) slid 2.83%, or 660.02 points, and posted its biggest drop since December 24, which had been the worst Christmas Eve performance for the index on record. The Nasdaq (^IXIC) declined 3.04%, or 202.34 points.

Any moves in Apple’s stock contribute heavily to shifts in the three major indices. Apple makes up nearly 10% of the tech-heavy Nasdaq and 3.4% of the S&P 500. And every $1 loss in Apple’s share price contributes to an about 6.8-point decline on the price-weighted Dow – as well as a $4.75 billion reduction in Apple’s market capitalization.

Apple shocked investors after market close Wednesday by pre-announcing it was lowering its revenue expectations for the fiscal first quarter 2019, which encapsulates the key holiday season. The tech giant lowered its quarterly revenue guidance to $84 billion from the $89 billion to $93 billion it projected earlier and shaved down its outlook for gross margins.

Apple’s stock slumped 9.96% to $142.19 per share as of market close Thursday.

An electronic screen displays Apple stock at the Nasdaq MarketSite in New York. Microsoft is threatening to overtake Apple as the world’s most valuable publicly traded company. AP Photo/Mark Lennihan, File)

Beyond the downwardly revised guidance, Apple’s justification for its revenue outlook reduction ignited investor concern. Apple CEO Tim Cook said in his letter to investors that demand for the company’s weakness in Greater China and other emerging markets contributed to the “vast majority of the year-over-year iPhone revenue decline,” and noted that “China’s economy began to slow in the second half of 2018.”

The explicit references to weakness in the world’s second largest economy was taken by many investors as further confirmation of a global growth slowdown. Apple’s announcement follows a slew of data from China pointing to weakening conditions in some of the country’s biggest industries. On Wednesday, the Caixin/Markit Manufacturing Purchasing Managers’ Index for China showed a reading of 49.7 in December from 50.2 in November, the first time since May 2017 that the reading fell below 50, indicating contraction in manufacturing activity.

Apple’s announcement also sent a jolt through currency markets. Art Cashin, managing director of UBS Financial Services, pointed out in a note Thursday that at about 9:30 a.m. in Sydney, Australia, a burst of buying hit the Japanese yen, a currency generally viewed as a safe haven investment. The yen shot up 8% higher against the Australian dollar in minutes, and nearly 10% higher against the Turkish Lira. Although the yen gave back half of those moves within the next half-hour, “it was historically a massive, massive move,” Cashin noted. The U.S. Dollar/Yen declined 3.4% at the lows of Wednesday evening, the biggest drop since November 2016.

STOCKS: Apple suppliers tank as iPhone-maker slashes guidance

Apple’s dismal revenue outlook announcement set off a domino effect of tumbling share prices among the iPhone maker’s suppliers. Shares of optical device-producer Lumentum Holdings (LITE) and semiconductor company Qorvo (QRVO) each tumbled more than 8% as of market close. Shares of AMS (AMS.VX), which provides optical sensors for smartphones’ 3D facial recognition, slumped 23%.

Bristol-Myers Squibb (BMY) announced on Wednesday that it plans to purchase biotechnology company Celgene (CELG) in a cash-and-stock transaction with an equity value of $74 billion. Based on terms of the agreement, Celgene shareholders will receive one Bristol-Myers Squibb share and $50 in cash per share, or $102.43 per share, representing a 54% premium to Celgene’s closing price Wednesday. The deal sets Bristol-Myers up to acquire a host of Celgene’s highly successful products, including blood-cancer therapy Revlimid, which generated more than $7 billion in sales through the first nine months of 2018. Shares of Celgene surged 20.69% to $80.43 each, while shares of Bristol-Myers Squibb fell 13.26% to $45.12 each as of market close.

Delta Air Lines (DAL) said in a statement Thursday that it is cutting its revenue forecast for the fourth-quarter of 2018. Delta said its fourth-quarter revenue from each seat flown per mile will rise 3% year-over-year, a 50-basis point reduction from the airline’s previous forecast. The metric is key indicator of future fare growth for airline companies. Delta also said that total revenue will increase 7%, lower than the 7.5% previously anticipated. Shares of Delta Air Lines declined 8.96% to $45.60 each as of market close Thursday, while shares of peer airline stocks Alaska Air Group (ALK), Southwest Airlines (LUV) and United Continental Holdings (UAL) also slid.

ECONOMY: U.S. adds more jobs than expected in December, according to ADP/Moody’s report

Private sector job creation surged more-than-expected in the U.S. for the month of December, according to the latest monthly results of the ADP/Moody’s Analytics survey released Thursday. U.S. companies added 271,000 new positions, exceeding consensus expectations of 180,000 new jobs and the downwardly revised 157,000 new positions created in November. Service-related industries comprised 224,000 new hires, with professional and business services coming out ahead with 66,000 new positions. The rosy results for non-farm private sector employment at the end of 2018 come amid concern of a slowing U.S. economy, and precede the Bureau of Labor Statistics’ monthly jobs report slated for release Friday, with consensus estimates calling for an addition of 180,000 new jobs.

“The 271,000 surge in the ADP measure of private employment in December provides further evidence that, for all the recent volatility in financial markets, the U.S. economy remains in a healthy shape going into 2019,” Andrew Hunter, chief U.S. economist for Capital Economics, wrote in a note Thursday. “The ADP survey hasn’t always been a particularly useful guide to the official non-farm payrolls figures, but this report suggests there may be some upside risk to our forecast that the December employment report, due tomorrow, will show a 180,000 gain in non-farm payrolls.”

Weekly jobless claims increased more-than-anticipated for the week ending December 29, according to the Department of Labor’s weekly report. New unemployment claims totaled 231,000 for the week, exceeding consensus estimates by 11,000 and the prior week’s results by 10,000. Continuing claims for the week ending December 22 also rose more-than-expected, registering at 1.74 million versus 1.69 million anticipated. For the week prior, continuing jobless claims were upwardly revised to 1.708 million.

U.S. manufacturing sector activity expanded at a slower pace than anticipated in December, based on the Institute of Supply Management’s monthly report. The headline index fell to 54.1 in December from 59.3 in November and fell short of consensus expectations calling for a reading of 57.5. Readings above 50 indicate expansion in manufacturing industry activity. Aside from the headline index, ISM’s readings for new orders, production, employment, supplier deliveries, inventories and prices in the manufacturing sector also slipped in December, with each index indicating expansion, but at slower pace. This is the latest index to point to slowing expansion in the U.S. manufacturing sector. On Wednesday, IHS Markit’s headline U.S. manufacturing purchasing managers’ index retreated to a 15-month low.

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Emily McCormick is a reporter for Yahoo Finance. Follow her on Twitter: @emily_mcck

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