The world has stopped and remembered the devastating terrorist attacks on September 11 2001 that changed the world forever.
Five years after hijackers in four passenger jets killed 2,973 people, a series of memorial events were taking place.
At Ground Zero in New York, relatives of those who died began gathering to leave flowers at the site where the World Trade Centre's twin towers were destroyed.
Firefighters whose colleagues died in the attacks also came to the building to remember those who gave up their lives while trying to save others.
Just before a moment's silence, led by mayor Michael Bloomberg, a choir sang the US national anthem as officers held up stars and stripes flags.
President George Bush spent the morning in the city having breakfast with firefighters and emergency workers. Later he will visit the Pentagon, also targeted by the hijackers, and the site in Pennsylvania where a fourth plane crashed. He will address the US from the Oval Office later this evening.
A moment of silence was taking place at the site where each crash took place.
Rudolph Giuliani, who was hailed for his courageous response to the disaster as mayor of New York, told ABC's Good Morning America that for the memory of the victims "we have to remain vigilant".
The ceremony was taking place under a sky as blue and clear as it was the day the terrorists struck in 2001. As the names of the dead were read, family members filed down a ramp to the bottom of the 70ft-deep pit to lay flowers at the footprints of the Towers.
Another moment of silence was held at 9.03am marking the time the South Tower was struck. In the bright sunshine an honour guard of firefighters and police officers, including 120 British bobbies, stood overlooking the site.
