Although it's been 23 years, the commemoration of Sept 11 remains uniquely somber, even in election years.

The morning after their heated presidential debate in Philadelphia, US Vice-President Kamala Harris, the Democratic candidate, and former president Donald Trump, the Republican candidate, stood in the same row in a Manhattan ceremony Wednesday morning along with current President Joe Biden. They listened to the annual reading of the names of the victims of the Sept 11, 2001, terrorist attacks.

Biden and Trump shook hands, as did the vice-president and Trump, whose running mate, Senator JD Vance of Ohio, also was there. Former New York mayor Michael Bloomberg stood in the middle of the politicians.

In describing the scene, The New York Times wrote that "it is a mark of the singular nature of Sept. 11 as a traumatic national touchstone that the combatants in today's scathing political wars would feel compelled to share a tent even for an hour".

"Both sides knew that whoever did not show would pay a political price, so they swallowed any reservations and made the appearance."

There were no formal remarks at the Ground Zero site, where on Sept 11, 2001, al-Qaida hijackers intentionally crashed two planes into the Twin Towers of the World Trade Center, both of which eventually collapsed.

Hijackers also crashed another jet into the Pentagon, and a fourth plane went down in a Pennsylvania field after passengers heroically stormed the cockpit and confronted the hijackers.

The attacks at the three sites claimed nearly 3,000 lives.

In New York, which took the brunt of the 9/11 toll, family members, including wives, husbands, sisters, brothers and now, more than two decades later, an increasing number of grandchildren, read out the names of the deceased.

As the years passed, scores of people who were at Ground Zero and lucky enough to survive that fateful day ended up succumbing to cancers and other diseases due to the toxic burning at the site. Many of them were volunteers who helped clear "the pile" of debris.

More than 45,000 people are living with physical ailments resulting from that day, the New York Post reported.

At least 45,200 civilians and officers from the Fire Department of New York (FDNY), the New York Police Department (NYPD) and the Port Authority of New York and New Jersey have at least one cancer or disease that has been directly linked to 9/11.

The FDNY lost 343 members on 9/11, many of whom headed into the building while others were fleeing. Now, the FDNY says that more firefighters have died from illnesses stemming from rescue and recovery efforts at Ground Zero.

Last week, the names of 32 FDNY members were added to the department's World Trade Center Memorial Wall in Brooklyn, putting the deaths from illnesses to more than 360, Axios reported.

"As we do every year, we will reflect on the 343 members who died that day, and we will be sobered in knowing that those insurmountable losses did not end at the World Trade Center site," Fire Commissioner Robert Tucker said during the Sept 4 ceremony. "Instead, we have seen our members become sick because of time they spent working in the rescue and recovery."

The NYPD lost 23 members on 9/11, but subsequent illnesses have claimed many more lives. In May, the Police Benevolent Association recognized 377 total members on its NYPD Memorial Wall as those who died from Sept 11-related illnesses, but said the number has already risen to more than 400, the New York Post reported.

Many financial industry workers at Wall Street firms such as Cantor Fitzgerald were killed, as the World Trade Center was located in the Financial District, a short walk from the New York Stock Exchange.

Biden, Harris and Trump also visited Shanksville, Pennsylvania, on Wednesday, where Flight 93 went down. The president called for a return to bipartisan unity and gave a hat to a Trump supporter, who gave him a Trump hat in return, according to spokesperson Andrew Bates.

The president put on the hat, making for a viral photograph. "Thanks for the support, Joe," the Trump campaign wrote on social media.

Biden and Harris later headed to a memorial at the Pentagon outside Washington.

"On this day 23 years ago, terrorists believed they could break our will and bring us to our knees. They were wrong. They will always be wrong. In the darkest of hours, we found light. And in the face of fear, we came together -- to defend our country, and to help one another," Biden said in a statement.

Trump told Fox News of Sept 11: "It was a very, very sad, horrible day. There's never been anything like it."

Agencies contributed to this story.