As he has every year since the terrorist attacks, Bush observed a moment of silence at 8:46 a.m. EDT, the exact minute in 2001 when hijackers smashed the first passenger jet into the World Trade Center.
He left the White House in the afternoon on his way to New Orleans, where he was spending the night on the amphibious assault ship USS Iwo Jima that is serving as the command and control center for relief efforts. The president made no comments upon his departure.
On Monday, Bush was to tour Gulfport, Miss.
It was the president's third trip to the region in the nearly two weeks since Hurricane Katrina and subsequent flooding obliterated wide swaths of the states.
The disaster has been a low point in Bush's presidency, with his job approval dipping to a record 39 percent in an Associated Press-Ipsos poll last week. Just over half of respondents said he is at fault for the slow response to the hurricane.
Democrats piled on the blame. Party leader Howard Dean on Sunday questioned why the federal government was not better prepared for Katrina after the experience of responding to the terrorist attacks.
"Sadly, the federal government's lack of preparation followed by its inept response had deadly consequences for far too many Americans in Katrina's path," Dean said in a statement. "The American people are counting on their leaders in Washington, D.C., to do better."
As Sunday's anniversary approached, Bush has linked the experience of Sept. 11 and Katrina in his speeches and his weekly radio address.