A woman pauses at the south reflecting pool at the National September 11 Memorial and Museum in lower Manhattan on the 16th anniversary of the 9/11 attacks in New York City, US, September 11, 2017. [Photo/Agencies]

At the Flight 93 National Memorial, Pence said the passengers who revolted against hijackers might well have saved his own life.

The Republican vice-president was a member of Congress on 9/11, and the Capitol was a possible target of the terrorist piloting Flight 93. Instead, it crashed near Shanksville after the passengers took action. Thirty-three passengers and seven crew members were killed.

At the United Nations, some ambassadors noted the anniversary as the Security Council unanimously approved new sanctions against the Democratic People's Republic of Korea in response to its Sept 3 test of what Pyongyang said was a hydrogen bomb.

"We will never forget the victims of Sept 11, and we will never forget the lesson that those who have evil intentions must be confronted," US Ambassador Nikki Haley said.

At dusk, the annual "Tribute in Light" art installation beamed two giant towers of light into the lower Manhattan skyline as a visual memorial to those who perished in the terror attack.

The ceremony on the National September 11 Memorial & Museum plaza in New York strives to be apolitical, allowing politicians to attend but not to speak. Yet last year's 15th anniversary ceremony became entangled in the presidential campaign when Democratic nominee Hillary Clinton left abruptly, stumbled into a van and ultimately revealed she'd been diagnosed days earlier with pneumonia.

This year, the focus remained on the names read out beneath the waterfall pools and lines of trees.

While many Americans may no longer interrupt their days to observe the 9/11 anniversary, the ceremony remains a touchstone for many victims' families and friends.

"I'll come every year for the rest of my life," said Rob Fazio, who lost his father, Ronald Fazio. "It's where I get my strength."

After 15 years of anniversaries, the reading of names, moments of silence and tolling bells have become rituals, but each ceremony takes on personal touches. Name-readers Monday gave updates on family graduations and marriages and remembered loved ones' flair for surfing or drawing on coffee-shop napkins.

A few never even got to know the relatives they lost on Sept 11, 2001.

"I wish more than anything that I could have met you," Ruth Daly said after reading names in remembrance of her slain grandmother and namesake, Ruth Lapin.

Delaney Colaio read names in honor of the three relatives she lost: her father, Mark Joseph Colaio, and her uncles, Stephen Colaio and Thomas Pedicini. Just a toddler on 9/11, she is now making a documentary about the children who lost parents in the attacks.

"I stand here as a reminder to the other families of 9/11 and to the world," she said, "that no matter how dark moments of life can get, there is light ahead if you just choose hope."

AP