U.S. stocks closed sharply lower Friday, locking in the worst 10-day start to a calendar year ever, as oil prices plunged and investors worried about slowing growth in the U.S.

During the course of the session, the S&P 500 broke below its Aug. 24 low—which several market strategists said would be tantamount to a major sell signal—to trade at its lowest level since October 2014. The Dow Jones Industrial Average was briefly down as much as 537 points.

Oil appeared to be the main driver of concern. Both the U.S. CLG26, UK:LCOG6 and global benchmarks settled below $30 a barrel, as investors feared that supplies will continue to rise as Iran prepares to enter the market ad Russia continues pumping oil to help support its flagging economy.

”There’s not a lot of people willing to take their foot off the gas and prices are adjusting accordingly,” said David Meier, portfolio manager at Motley Fool Asset Management. “As a result of that you’re seeing fear just creep in.”

The Dow DJIA, -0.01% slumped 390.97 points, or 2.4%, to 15,988.08, while the S&P 500 SPX, -0.23% slid 44.85 points, or 2.3%, to 1,876.99, led lower by the financial, technology and energy sectors. The Nasdaq Composite COMP, -0.28% tumbled 126.59 points, or 2.7%, to 4,488.42.

All Dow components ended in negative territory, as were all 10 sectors on the S&P 500.

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Read:Why oil could plunge to $20 a barrel, but probably not $10

Selling began in China after official data showed that new bank loans were lower than expected in December as lenders sharply curtailed activity amid worries about slowing growth and bad debt. In a bid to boost liquidity, China’s central bank said it pumped $15 billion of funds into the market via a medium-term lending facility on Friday.

The Shanghai Composite SHCOMP, +2.06% dropped 3.5% and is down 20% from a Dec. 22 high, which by one definition puts it in a bear market.

All of this was exacerbated as options stopped trading ahead of their expiration on Saturday. Dave Lutz, head of ETFs at JonesTrading, said because of how the market was positioned, options dealers needed to sell more futures to hedge their positions as stocks fell.

Intel Corp. INTC, -0.51% was the biggest loser among Dow components, plunging 8.9%, after earnings late Thursday, and major oil companies Chevron Corp. CVX, -0.14% and Exxon Mobil Corp. XOM, -1.12% also were big losers.

Both the Dow and S&P 500 finished the week down more than 2%, while the Nasdaq shed more than 3% of its value this week.

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Economic signals: A spate of disappointing U.S. data show that both manufacturing and consumer spending are in trouble. Empire State factory index declined sharply in January to its lowest level since the recession. Retail sales declines by 0.1% in December a report on industrial production compiled by the Federal Reserve showed that activity declined for the third straight month.

The cost of producing goods and services dropped again.

The lone bright spot was a report on consumer sentiment in January, which rose to 93.3 from a preliminary reading of 92.6 in the University of Michigan’s preliminary January reading.

Read: Why U.S. retail sales will be weak again in December

New York Fed President William Dudley remained upbeat when he spoke Friday, saying he still expected the economy to push the unemployment rate down further and for growth to be slightly above the long-term trend.

Stocks to watch: Despite J.P. Morgan Chase & Co.’s JPM, +0.01% upbeat results, the bank’s shares were off 2%.

Shares of BlackRock Inc. BLK, +1.48% were down 4.3% even after the firm said its earnings rose on the back of higher fees.

Wells Fargo & Co. WFC, +0.83% shares were 3.6% lower, after the bank posted a profit that was flat as low oil prices hurt the country’s fourth-largest bank by assets.

Citigroup Inc. C, -0.54% profit soared last quarter as litigation costs fell. But its shares were ended 6.4% lower.

Shares of Analog Devices Inc. ADI, -0.42% slumped 1.4% after it cut its revenue outlook late Thursday.

General Electric Co. GE, +0.70% said it has made a deal to sell its appliance unit to Shanghai-listed Qingdao Haier Co. 600690, +2.43% , in which Chinese appliance maker Haier Group owns a key stake, for $5.4 billion. Shares of GE finished down 2%.

Other markets: European stocks were unable to escape the downward trend from other markets, and the Stoxx Europe 600 index SXXP, -0.42% lost 2.8%. The dollar USDJPY, -0.41% fell to a one-year low vs. the yen. Gold US:GCG6 rose $22.40, or 2.1%, to $1,096.20 an ounce.