Dozens of family members and colleagues filled the pews as the Port Authority Police Pipes and Drums played during the posting of colors.
Around the world, thousands of volunteers pledged to do good deeds, honoring an anniversary that was designated a National Day of Service and Remembrance in 2009.
By next year's anniversary, a 9/11 museum is expected to be open beneath the memorial plaza in New York City. While the memorial honors those killed, the museum is intended to present a broader picture, including the experiences of survivors and first responders.
"As things evolve in the future, the focus on the remembrance is going to stay sacrosanct," memorial President Joe Daniels said.
Douglas Hamatie, whose 31-year-old cousin Robert Horohoe worked for Cantor Fitzgerald and died on 9/11, drew applause from the crowd when he declared that the day should become a national holiday.
"The kids today, they know when the next iPhone's coming out, and they know when the next Justin Bieber concert is, but they don't know enough about 9/11," he said. "So let's change that, please."
The organizers have said they will always keep the focus on the families, and that was evident this year as relatives gathered on the tree-laden plaza, where a smaller crowd gathered — only friends and family of the victims were allowed.
Vicki Tureski, who lost her brother-in-law on Sept. 11, said the victims' families will help each other through the years to come.
"Strangers who are now friends, friends who are now family, family who pull us to our feet each day," she said. "I promise to continue to keep you in my prayers as we go through decade two of carrying the tragedy of 9/11 with us."
Associated Press writers Verena Dobnik, Jennifer Peltz and Colleen Long in New York, Nedra Pickler in Washington, Matthew Barakat in Arlington, Va., and Kevin Begos in Shanksville, Pa., contributed to this report.
- Rubber chickens, afros and clowns: A look at...
- Why Utahns are some of the biggest spenders,...
- Ferguson protesters across US peaceful,...
- Steven Powell ordered to serve more jail time...
- As Ferguson verdict is read, protesters in...
- Immigration reform will boost the economy,...
- UC students walk out to protest tuition hikes
- In Britain, US turkey dinner is big for business
- As Ferguson verdict is read, protesters... 68
- Grand jury won't indict Ferguson cop in... 30
- Obama: Americans want 'new car smell'... 29
- Winners and losers under Obama's... 18
- Ferguson businesses torched in... 17
- Under pressure, Hagel steps down as... 15
- Obama immigration plan good, not great... 13
- Obama heads to Chicago to pitch... 13