The S&P 500 eked out a small gain for a third straight session on Thursday, helped by a flurry of merger activity, though investors see no catalysts to lift the market further with major averages near multi-year highs.

The market's slowed advance took the S&P 500 to its highest intraday level since November 2007 on Wednesday. While the index notched its third straight day of gains, none was more than 0.2 per cent.

Shares of H.J. Heinz Co jumped 20 per cent to $US72.50 after it said Warren Buffett's Berkshire Hathaway and 3G Capital will buy the food company for $US72.50 a share, or $US28 billion including debt. Berkshire's class B shares rose 1.3 per cent to $US99.21.

Also supporting the market was data showing the number of Americans filing new claims for unemployment benefits fell more than expected in the latest week. The CBOE Volatility index fell 2.4 per cent, dropping to 12.67.

"While I'm not bearish, I don't see many upside motivations at these levels," said Donald Selkin, chief market strategist at National Securities in New York, who cited the low level of the VIX as a sign the market was overbought.

Equities have struggled to break above current levels where they have been hovering for almost two weeks. The S&P 500 is up more than 6 per cent so far this year.

"We need to digest some of our gains to go higher, but people are so eager to buy on the dips that we're not even seeing dips anymore. People are just chasing the market higher," said Selkin, who helps oversee about $US3 billion in assets.

Stocks fell earlier after a report the euro zone's gross domestic product contracted by the steepest amount since the first quarter of 2009. In addition, Japan's GDP shrank 0.1 per cent in the fourth quarter, crushing expectations of a modest return to growth.

The Dow Jones industrial average was down 9.52 points, or 0.07 per cent, at 13,973.39. The Standard & Poor's 500 Index was up 1.05 points, or 0.07 per cent, at 1,521.38. The Nasdaq Composite Index was up 1.78 points, or 0.06 per cent, at 3,198.66.

Constellation Brands soared 37 per cent to $US43.75 after AB InBev's deal to take over Mexican brewer Grupo Modelo was revised to grant Constellation perpetual rights to distribute Corona and other Modelo brands in the United States. US shares of AB InBev gained 5.1 per cent to $US92.77.

American Airlines and US Airways Group said they plan to merge in a deal that will form the world's biggest air carrier, with an equity valuation of about $US11 billion. US Airways shares fell 4.6 per cent to $US13.99.

Weakness in Europe contributed to a 5 per cent drop in revenue from the region for Cisco Systems, which nonetheless beat estimates as it reported its results late Wednesday. The company's shares dipped 0.7 per cent to $US20.99.

General Motors Co reported a weaker-than-expected fourth-quarter profit, also citing bigger losses in Europe alongside lower prices in its core North American market. The stock was off 3.3 per cent to $US27.73.

Only five more stocks rose than fell on the New York Stock Exchange, while 51 per cent of Nasdaq-listed shares closed higher.

Volume was light, with about 6.36 billion shares changing hands on the New York Stock Exchange, the Nasdaq and NYSE MKT, below the daily average so far this year of about 6.48 billion shares.

Reuters