The ceremony was as usual punctuated by poignant moments of silence, the first one coming at 1246 GMT, when the first plane hit one of the Twin Towers
US President Donald Trump struck a somber tone Friday on the anniversary of the September 11, 2001 attacks as his Democratic rival Joe Biden comforted relatives of victims -- in duelling bids to unite a deeply-divided nation.
Nineteen years after the devastating Al-Qaeda attacks, former vice president Biden began the day in New York for an annual event honouring the nearly 3,000 who died in the destruction of the World Trade Centre.
Trump did not attend the ceremony in his home city, sending Mike Pence instead. Biden and the vice president tapped elbows and chatted briefly.
The Republican president instead travelled to Shanksville, Pennsylvania, where an airliner crashed after passengers tried to wrest control of the jet from the hijackers.
The president and First Lady Melania Trump listened in silence as the names of the 40 passengers and crew killed aboard Flight 93 were read aloud -- with two bells tolling after each.
In brief prepared remarks, the incumbent -- who is hoping to defeat Biden and win a second term -- paid "tribute to their sacrifice" along with all those who perished in the attacks.
He also honoured first responders as well as military personnel who fought to "preserve our freedom" in the subsequent wars launched under former president George W. Bush.
"We resolve to stand united as one American nation, to defend our freedoms, to uphold our values, to love our neighbours, to cherish our country.... and to never, ever forget," Trump said.
It was a rare call for unity from a leader who normally plays political divisions to his advantage.
Biden also travelled to Shanksville but there was no chance of the rivals crossing paths, as Trump left well before the Democratic candidate and his wife Jill arrived.
As a few hundred spectators watched from the Flight 93 national memorial park, Biden laid a wreath of white flowers at the stone bearing the victims' names.
He and Jill again spoke with families, later meeting with local firefighters to whom the couple brought sweets and beer.
Biden connects with relatives
At his first stop in New York, Biden did not deliver a speech -- the ceremony generally reserves that privilege to the close ones of victims -- but his mere presence drew attention at an event broadcast live on main US television networks.
The ceremony was as usual punctuated by poignant moments of silence, the first one coming at 1246 GMT, when the first plane hit one of the Twin Towers.
The 77-year-old Biden -- wearing a mask -- appeared in his element at the relatively crowded event, surrounded by people after months of keeping a low profile in line with coronavirus prevention measures.
At one point, he sought common ground with a 90-year-old woman whose son died at age 43 in the attacks, reflecting on the loss of his own son Beau to cancer.