A final steel beam has been placed on World Trade Center Tower 4 ahead of its inauguration next year, making it the first rebuilt structure at the site of the September 11 attacks to be topped off.
An American flag fluttered from the beam as construction workers hoisted it to the top of the 72-story building in an emotional ceremony on Monday.
The construction of the 977-foot (293-metre) tower, designed by Japanese architect Fumihiko Maki, began in 2008.
"The topping out of 4 World Trade Center represents another milestone in the effort to create a new, dynamic World Trade Center at the heart of a resurgent Downtown," project developer Larry Silverstein said at the ceremony.
The unfinished skeleton of the nearby Freedom Tower is already the tallest building in New York City and is set to reach a symbolic height of 1,776 feet (541 meters), the year of US independence.
Some 3,000 people were killed in the attacks on September 11, 2001 when Al Qaeda hijackers plowed two planes into the World Trade Center and a third into the Pentagon, while a fourth plane was brought down in a Pennsylvania field after passengers overpowered their attackers.
Today the New York site includes two fountains sunk into the footprints of the former Twin Towers, with the names of the dead inscribed around the edges.