US stock markets reopened on Wednesday after a historic two-day closure forced by superstorm Sandy, which completely shut down the global financial center of New York.

Even though much of New York City was still suffering the effects of power outages, flooding and wind damage, trade was smooth on the New York Stock Exchange and the Nasdaq exchange following the markets' first closure since the September 11 attacks of 2001.

NYSE Euronext chief executive Duncan Niederauer told CNBC television that the exchange systems were working smoothly, and that even with the power outages, the exchange could operate smoothly full-time on its own backup generators.

"They're all working, everything is fine," he said.

Fifteen minutes into trade the Dow Jones Industrial Average was up 65.28 points (0.50%) to 13,172.49.

The broad-based S&P 500 gained 4.56 points (0.32%) to 1,416.50, while the Nasdaq was down 4.01 (0.13%) at 2,983.94.