"Earnings have been ok – this momentum just shows you the strength of the bulls, driven by Uncle Ben (Bernanke)," said Uri Landesman, president of Platinum Partners, referring to the Federal Reserve's bond-buying program. "When the Fed's pump gets taken out of the mouth of the balloon, that's when it will pop or fly around the room. We have yet to see the correction, which will probably happen between now and the end of October."
So far, just about a half of S&P 500 companies have reported quarterly results this quarter, with 68 percent of firms posting earnings that have beat estimates, according to the latest data from Thomson Reuters. If all remaining companies report earnings in line with estimates, earnings will be up 3.6 percent from last year's first quarter.
Meanwhile, only 41 percent of companies have beaten their revenue expectations.
(Read More: Earnings Watch: Revenue Shortfalls Continue)
Starbucks, Amazon, Expedia, Baidu and Coinstar are among notable companies scheduled to post earnings after the closing bell.
The Chicago Board Options Exchange reopened trading on all its products at 1pm ET after a system outage. Trading in options on the S&P 500 index and the CBOE volatility index were among those affected.
"As we enter this high-speed algo-model-type of world that we're in, things just happen quicker and faster," said Brian Stutland, managing member at Stuland Volatility Group. "We even saw the in the [AP Twitter] hack attack [on Tuesday]–Vix futures moving 10 percent up and down within 4 minutes—the guys on the floor didn't even get a chance to react to such movements. So some of these issues we need to take step by step in how fast we're advancing in this area of trading."
On the economic front, jobless claims declined 16,000 last week to a seasonally adjusted 339,000, according to the Labor Department. Analysts had expected 351,000 new claims last week, according to a Reuters poll.
In other stock news, Verizon Communications hired advisors to prepare a $100 billion cash-and-stock-bid to take full control of Verizon Wireless from Vodafone, Reuters reported, citing sources familiar with the matter.
Gold climbed to its highest in 10 days, helped by a weaker dollar and firm prices in other commodities. Traders also cited support from central bank buying after IMF showed that Russia and Turkey had continued to add to their holdings in March.
(Read More: From Rout to Rush—Gold Stages Quiet Rally)
In the bond markets, the Treasury auctioned $29 billion in 7-year notes at a high yield of 1.155 percent. The bid-to-cover ratio, an indicator of demand, was 2.71.
Across the Atlantic, European shares rose after the U.K. posted better-than-expected first quarter GDP numbers, helping the country avoid a triple-dip recession.