A museum memorialising the September 11, 2001 attacks on New York, Washington and Pennsylvania has opened to family members of the victims who died in the attacks.
The museum, which will open to the public on May 21, is the culmination of eight years' work and countless disputes over how to document the day when hijacked planes flew into the World Trade Centre, the Pentagon and an open field near Shanksville, Pennsylvania, killing close to 3,000 people.
"The museum is a place where you can come to understand 9/11 through the lives of those who were killed and the lives of those who rushed here to help," said Michael Bloomberg, New York's former mayor, as he introduced the museum to members of the media on Wednesday.
It is incredible, and it will wind up affecting different people in different ways, depending on their experiences.
The museum tries to convey the events and emotions of September 11 by using audio, such as telephone messages left to loved ones from those who later died in the towers and cockpit recordings from the planes.
It also includes exhibits like a mangled fire truck, a memorial wall with photos of victims and video footage of the towers collapsing.
Some 35,000 people were closely involved in creating the museum, including victims' families.
"It is incredible, and it will wind up affecting different people in different ways, depending on their experiences," said Joel Shapiro, whose wife, Sareve Dukat, died in the South Tower.
US President Barack Obama praised the museum, calling it "a sacred place of healing and hope".
"It's an honour to join in your memories, to recall and to reflect, but above all to reaffirm the true spirit of 9/11 - love, compassion, sacrifice - and to enshrine it forever in the heart of our nation," Obama told an audience of victims' relatives, survivors, and rescuers at the ground zero museum's dedication ceremony on Thursday.
More than half of the $700m needed to build the museum and memorial was raised privately and about $250m came from federal disaster funding.
The museum also commemorates the 1993 bombing of the World Trade Centre.