Stock index futures stopped trading electronically at 9:15 a.m. ET and will stay shut until further notice.

NYSE Euronext and Nasdaq OMX Group said they made their decision in consultation with industry executives and regulators, and intend to reopen Wednesday, conditions permitting.

"It doesn't make sense to put people in harm's way or to only have half a market," said Nicholas Colas, chief market strategist at ConvergEx Group in New York. "If just the electronic market was open, that wouldn't provide enough interest, with everything else still closed."

The hurricane has already forced thousands to seek higher ground, halting public transport and closing schools, businesses, and government departments.

Italian political turmoil and Spanish hesitancy over seeking euro-zone assistance put the two countries on the front line of the region's debt crisis and back under market pressure on Monday as their leaders met in Madrid.

"We have an illiquid market, we have a risk-off situation from overseas, and we have some issues going on in the States with Sandy, so that is impacting things a little more than expected," said David Lutz, managing director of trading at Stifel Nicolaus Capital Markets in Baltimore.

Futures closed well off their session lows. S&P 500 futures fell more than 10 points at the intraday low. Futures will not reopen as usual during the day, including the popular S&P 500 e-mini contract that lets smaller traders access index futures.

E-mini contracts typically trade around the clock, closing for just 45 minutes of each day.

A market closure for more than a day may start causing problems for investors who need to trade in and out of positions, investors said.

"If you go two days, you really start to create some serious financial stress for some players that need to get something done," said Jim Paulsen, chief investment officer of Wells Capital Management in Minneapolis. "A two-day closure will create more stress, and therefore will allow electronic trading. That's my best guess."

Wall Street banks, including Goldman Sachs and Citigroup, activated their emergency plans, which many firms put in place after the Sept. 11, 2001, attacks. Banks were putting key staff, including some traders, in hotels and also are relying on others who live near the bank's offices.

Some offices in lower Manhattan's Financial District are in evacuation zones and most non-critical staff and employees who don't rely on high-speed systems, including some investment bankers, were asked to work from home.

CME Group closed its interest rate operations, including Treasury, Eurodollar and fed funds futures and options on futures markets on the trading floor at noon on Monday in line with a closure of the cash market.

The Securities Industry and Financial Markets Association said earlier on Sunday it is recommending an early close of noon EDT on Monday for the trading of U.S. dollar-denominated, fixed-income securities. It said its member firms should decide for themselves whether their fixed-income departments remain open for trading.

The foreign-exchange market's activity generally follows the fixed income markets.

The U.S. Federal Reserve said it would postpone its regularly scheduled releases, including its weekly report on selected interest rates and daily commercial paper data. The Fed said it would release the data when federal offices in the Washington area reopened.

Wall Street was spared the worst of Hurricane Irene in August last year. Officials had feared Irene would flood lower Manhattan and cripple business in the world's financial capital, but the flooding was minor and there were no major disruptions at the exchanges.

On Tap This Week:

TUESDAY: S&P Case-Shiller home price index, consumer confidence, Fed's Kocherlakota speaks

WEDNESDAY: Weekly mortgage apps, Chicago PMI, oil inventories, farm prices

THURSDAY: Challenger job-cut report, ADP employment report, jobless claims, productivity and costs, ISM mfg index, construction spending, auto sales, chain-store sales, Facebook's "gifts" event, Fed's Lockhart speaks, Fed's Rosengren speaks

FRIDAY: Non-farm payrolls, factory orders, Fed's Williams speaks, Wynn shareholders meeting

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