Americans are commemorating 9/11 with tributes that have been altered by coronavirus precautions and woven into the presidential campaign.
President Donald Trump and Democratic challenger Joe Biden will pay their respects at the same memorial without crossing paths.
In New York, victims’ relatives began gathering for split-screen remembrances, one at the September 11 memorial plaza at the World Trade Centre and another on a nearby corner, set up by a separate 9/11-related organisation.
The Stephen Siller Tunnels to Towers Foundation objected to the memorial’s decision to forgo a longstanding tradition of having relatives read the names of the dead, often adding poignant tributes. Memorial leaders said the change for the 19th anniversary of the terror attacks was a coronavirus safety precaution.
Kathy Swift arrived early at the alternative ceremony, wearing a T-shirt honouring her killed brother, Thomas Swift, who worked in finance.
“We still have to remember,” said Ms Swift. “The whole country’s going downhill. It’s one thing after another, and now with the Covid. I’m glad they’re still having this, though.”
Mr Trump and Mr Biden are both headed — at different times — to the Flight 93 National Memorial near Shanksville, Pennsylvania.
Vowing to never forget the nearly 3,000 people who died on 9/11, Mr Trump tweeted that the United States is honouring a commitment made in 2001 to always remember the “innocent Americans who were senselessly killed”.
The anniversary of 9/11 is a complicated occasion as the US grapples with a health crisis, searches its soul over racial injustice and prepares to choose a leader to chart a path forward.
Still, 9/11 families say it is important for the nation to pause and remember the hijacked-plane attacks at the trade centre, the Pentagon in Washington and near Shanksville in 2001.
Mr Biden initially attended the observance at the 9/11 memorial in New York, where he and vice president Mike Pence, wearing masks, exchanged an elbow bump each at ground zero before the ceremony began with the usual tolling of a bell.
Mr Biden offered condolences to a woman he spotted crying in the crowd of hundreds, Amanda Barreto, who lost her aunt and godmother in the attacks.
Ms Barreto, 27, said Mr Biden “wanted to let me know to keep the faith” and “wanted me to say strong”, telling her he understood what it meant to lose a loved one.
His first wife and their daughter died in a 1972 car crash, and his son Beau died of brain cancer in 2015.
Mr Biden did not speak at the ceremony, which has a longstanding custom of not allowing politicians to make remarks.