US President Joe Biden is attending a ceremony in New York to mark the 20th anniversary of the September 11th attacks.
Nearly 3,000 people were killed when four planes were hijacked and flown into the twin towers, the Pentagon and a field in Pennsylvania.
The ceremony at ground zero was started by a choir singing the American national anthem, followed by a minute’s silence.
The relatives of the victims are reading out the names of every person who lost their lives.
And bells have tolled at the exact moment the jets hit the twin towers.