One of Citigroup's downtown New York offices damaged by Hurricane Sandy will be closed for weeks, the company said Tuesday.

"Our facility at 111 Wall Street experienced severe flooding and will be out of commission for several weeks," Chief Executive Michael Corbat wrote in a memo to employees. "We are still assessing when other sites that were not damaged, including 388 and 390 Greenwich Street, can reopen."

Continued power outages, lack of mass transportation and mandatory evacuation orders make decision-making difficult, Corbat wrote. For the time being, Citi will rely on back-up sites and work-from-home strategies.

Citigroup (NYSE: C) was hoping to reopen some Northeast branches, including those in Washington, by Tuesday afternoon. It was deciding whether it can open branches in the New York area and other affected states on Wednesday.

Citi will take steps to help customers hurt by the storm, Corbat wrote. "We are helping clients with financial recovery solutions, providing access to cash and waiving certain fees, including those on wires to affected customers, early [certificate-of-deposit] withdrawals and overdrafts," his memo said.

"As difficult as the last few days have been, the next few are just as important and will surely present challenges," he wrote. "I know we will meet them with the same level of determination, thoughtfulness and sound judgment that you have exhibited throughout this event."

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