President Joe Biden made an unannounced stop Saturday afternoon at the Shanksville Volunteer Fire Department -- the first to respond to the United Flight 93 crash in Shanksville, Pennsylvania, on Sept. 11, 2001.

The president spent nearly an hour taking photographs and speaking with over 100 first responders and their families.

After his visit, Biden spoke briefly with reporters, where he reflected on the importance of memorials, like the ones erected in Shanksville to commemorate the victims of the 9/11 attacks.

“These memorials are really important, but they're also incredibly difficult for the people who were affected by them because it brings back that moment you got the phone call. It brings back that instant you got the news, no matter how many years go by," he said.

Unprompted, Biden said he thought former President George W. Bush gave a "really good speech" Saturday about about who Americans are.

"The core of who we are is not divided," Biden said.

When asked how the nation can get back to that state of unity, Biden said, “By being honest when I make a mistake. By being straightforward, telling people exactly what I want to do.”

-ABC News' Justin Gomez

The families of victims of both the Sept. 11 attacks and the 1993 bombing at the World Trade Center concluded their annual reading of the names.

The ceremony concluded with a performance of "Taps."

At sundown, the annual “Tribute in Light” will once again illuminate the sky in commemoration of the anniversary.

President Joe Biden and first lady Jill Biden arrived at the Sept. 11 memorial services at Shanksville, Pennsylvania.

The president laid a wreath at the Flight 93 National Memorial and silently reflected in front of the wall with the names of the 40 victims.

The Bidens walked the grounds of the memorial and spoke with family members of the victims who were in attendance.

Vice President Kamala Harris spoke at the Sept. 11 memorial service at Shanksville, Pennsylvania and reflected on the heroism of the passengers who fought the hijackers.

"What happened on Flight 93 told us then, and it still tells us so much about the courage of those on board who gave everything they possibly could, about the resolve of the first responders who risked everything and about the resilience of the American people," she said.

Harris said Sept. 11, 2001 showed the power of unity among strangers and that sentiment is still powerful 20 years later. The vice president called on Americans to continue that camaraderie.

"In a time of outright terror, we turned toward each other. In the face of a stranger, we saw a neighbor and a friend. That time reminded us the significance and the strength of our unity as Americans, and that it is possible in America," she said.