Relatives of victims killed at the World Trade Center gathered at ground zero in lower Manhattan for readings from dignitaries and a recitation of the names of the dead. Later Thursday, presidential candidates Barack Obama and John McCain were due at ground zero to pay silent respects.
"Today marks the seventh anniversary of the day our world was broken," Mayor Michael Bloomberg said. "It lives forever in our hearts and our history, a tragedy that unites us in a common memory and a common story ... the day that began like any other and ended as none ever has."
The ceremony at ground zero included moments of silence at 8:46 a.m. and 9:03 a.m. -- the times that two hijacked jets slammed into the twin towers. Two more moments of silence were to be held at the times the towers fell. Services were also being held in Pennsylvania and at the Pentagon, where a new memorial will be dedicated.
Relatives of victims began arriving at dawn at ground zero, now a huge construction site. American flags were draped over silent cranes.
Maureen Hunt, wearing a T-shirt with a picture of her sister, Kathleen, a 9/11 victim, said that it was comforting to be at the ceremony with so many who have lost loved ones.
"This is a place for us to meet," said Hunt, who has come each year to pay her respects. "It is not getting easier to attend these ceremonies."
Family members and students representing more than 90 countries that lost victims on Sept. 11 read the names of 2,751 people killed in New York, one more than last year. The city restored Sneha Philip, a woman who mysteriously vanished on Sept. 10, 2001, to its official death toll this year after a court ruled that she was likely killed at the trade center.
Among the readers was Laraine Angeline, who lost brother-in-law, Steve Pollicino. "Steve, your smiles live on with us," she said. "Our separation is temporary. Our love for you is forever."
McCain and Obama planned to visit the site after the ceremony concluded Thursday afternoon. The candidates agreed weeks ago to pull their campaign ads for the day and were appearing together Thursday night at a forum on volunteerism and service.
Former Mayor Rudy Giuliani was to speak at the ceremony, as he has every year in New York, along with officials including Bloomberg and Homeland Security Secretary Michael Chertoff.
Last year's reading by Giuliani, then a Republican presidential candidate, drew protests from family members who said the city was ill-prepared for the terrorist attacks under his leadership and questioned whether he should be there while running for the White House. They had no opposition to McCain and Obama' visit this year.
In Arlington, Va., Defense Secretary Robert Gates was scheduled to speak at a ceremony dedicating the memorial at the Pentagon, the first of three major Sept. 11 memorials to be completed.
The 2-acre park, located at the spot where American Airlines Flight 77 crashed into the Pentagon's west wall, consists primarily of 184 cantilevered benches, each bearing a victim's name.
President Bush and first lady Laura Bush marked the anniversary during a moment of silence on the South Lawn of the White House. The president was then to head to the Pentagon memorial.
In Pennsylvania, at least 200 people gathered Thursday morning at an observance in a reclaimed minefield in Shanksville where Flight 93 came down after passengers reportedly stormed the cockpit to thwart terrorists' plans to use that plane as a weapon like the others. Bells were to toll and victims' names would be read as part of the service.
McCain was also attending the memorial service in Shanksville for the 40 people killed aboard the hijacked flight.
Memorials are years away from being built in Pennsylvania and New York. As in past years, two bright blue beams of light will shine at night on the New York City skyline, in memory of the fallen towers.