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In this image taken with a cellphone by Jason McLane, the primary presidential aircraft, a Boeing 747 known as Air Force One when the president is aboard, flies low over New York Harbor, followed by an F-16 chase plane during a federal government photo op on Monday. ((Associated Press/Jason McLane))

A low-flying Boeing 747 sometimes used by the American president was escorted over lower Manhattan by two fighter jets as part of a U.S. government photo opportunity Monday, causing a brief panic among workers near Ground Zero.

John Leitner, a floor trader at the New York Mercantile Exchange Building, said workers received no official prior announcement about the exercise.

He said everyone raced for the exits when they saw the low-flying planes at around 10 a.m. ET, mere blocks from the former World Trade Center site that was hit by two hijacked passenger jets on Sept. 11, 2001.

"Everyone panicked, as you can certainly understand," Leitner said.

About 1,000 workers gathered along the Hudson River until a security officer with a bullhorn told them it was a planned exercise. Workers in other office buildings also reportedly spilled out into the streets.

The Federal Aviation Administration said the government was conducting a military photo op involving two Air Force F-16 jets and the 747, which is dubbed Air Force One when U.S. President Barack Obama is aboard. It said it had notified city law enforcement about the mission.

The New York Police Department said the flight "was authorized by the FAA for the vicinity of the Statue of Liberty, with directives to local authorities not to disclose information about it, but to direct all inquiries to the FAA Air Traffic Security Co-ordinator."

White House military office director Louis Caldera, whose office oversees all military operations aboard Air Force One on presidential trips, apologized in a statement Monday for the confusion and disruption.

Among the workers who left their buildings were some at The Wall Street Journal.

Kathleen Seagriff, a staff assistant in the newspaper's newsroom, said workers heard the roar of the planes and then saw them from their windows.

"They went down the Hudson, turned around and came back by the building," she said. "It was a scary scene, especially for those of us who were there on 9/11."