NEW YORK (TheStreet) -- Stocks slumped in the final hour of trading with the S&P 500 and Dow Jones Industrial Average struggling to hold onto April's gains. The Nasdaq was dragged down by a selloff among biotech stocks. 

The S&P 500 fell 1.3%, the Dow declined 1.3%, and the Nasdaq was down 1.8%. Markets fell in choppy trading as Wall Street digested key earnings reports from the likes of Nokia (NOK), Royal Dutch Shell (RDS.A) and Yelp (YELP). 

"Investors appear to be on edge, lacking conviction as to the most prudent near-term course of action and understandably so," said Terry Sandven, chief equity strategist at U.S. Bank Wealth Management, in a call. "The U.S. economy is navigating through a soft patch. The year-to-date performance has been lackluster and equities have been trending near all-time highs while earnings are being reset lower."

Celgene (CELG) led biotech losses after missing quarterly sales estimates and reiterating full-year guidance. Regeneron Pharmaceuticals (REGN) and Alexion Pharmaceuticals (ALXN) were lower, while the iShares Nasdaq Biotechnology Index ETF (IBB) slid 2.8%. 

Apple (AAPL) dropped more than 2% after the company disclosed the European Commission could require Ireland to recover past taxes over the past decade. The world's largest company said such tax payments could be "material."

In addition, The Wall Street Journal reported a key component of the Apple Watch made by one of two suppliers was found to be defective, limiting the availability of the new product.

Microsoft (MSFT), Google (GOOGL), Facebook (FB), Alibaba (BABA) and Oracle (ORCL) were all lower, while the Technology SPDR ETF (XLK) tumbled 1.7%.

Nokia and Alcatel-Lucent (ALU) were both lower. Nokia tumbled after reporting quarterly profits far below market expectations, raising concerns over its planned takeover of French telecom Alcatel-Lucent.

Major oilers suffered a big drop in revenue over the quarter as lower oil prices ate into the topline. Royal Dutch Shell reported a 56% decline in first-quarter earnings. Exxon Mobil  (XOM) reported revenue of $67.62 billion, down 36.7% from a year earlier. Marathon Petroleum (MPC) also saw a double-digit decline in quarterly sales. 

Colgate-Palmolive (CL) and Avon Products (AVP) were both lower after quarterly revenue came in lower on a stronger U.S. dollar. Pinnacle Foods (PF) was higher after guiding for a 7% to 10% increase in earnings for the full year. 

Time Warner Cable (TWC) was lower after missing quarterly estimates on its top- and bottom-lines. The cable giant earned $1.65 a share, lower than an estimated $1.88. Sales climbed 3.5% to $5.78 billion, below expectations for $5.83 billion.

Yelp (YELP) shares plummeted 23.9% after issuing weak guidance in its second quarter and full year. Second-quarter revenue is expected between $131 million to $134 million, below estimates of $138.4 million.

Sony (SNE) shares slid 1.3% after reporting a net loss of 126 billion yen over fiscal 2015, its sixth loss in seven years as it faces troubles in its smartphone business and the fallout from hacking attacks.

Air Products & Chemicals (APD) sank nearly 5% after reporting in-line quarterly earnings, while revenue tumbled 6.2% to $2.42 billion, missing estimates. (CRM) backed off of a 11.6% surge Wednesday afternoon after Bloomberg reported the company is working with financial advisers to field takeover offers. Shares fell 3.1% on Thursday.

Real personal income dipped 0.2% in March compared to an expected increase of 0.2%. Personal income increased 0.3% in February. Initial jobless claims for the week ended April 24 dropped 34,000 to 262,000. Economists had expected a reading of 288,000 after 296,000 a week earlier.

Japan's Nikkei closed nearly 3% lower after the Bank of Japan left interest rates unchanged, as economists had expected. Meanwhile, China's Shanghai Composite dropped 0.78% after steel demand fell 6% in the first quarter, the first decline for that quarter in the past 20 years.

European markets were all lower despite eurozone deflation pausing in April. The region's Consumer Price Index was flat in April, its first neutral reading after months of negative data. German unemployment fell in April, though at a slower-than-expected pace.