Thousands gather at World Trade Center in New York on 9/11 anniversary

Thousands have gathered at Ground Zero in Manhattan, New York on Tuesday (local time) to mark the 17th anniversary of the September 11 terror attacks that destroyed the Twin Towers at the World Trade Center.

Six moments of silence were observed throughout the morning.

The first at 8:46am was when hijackers flew American Airlines flight 11 into the North Tower, and that was followed by another at 9:03am to mark the moment United Airlines flight 175 flew into the South Tower.

Further moments of silence marked the time each building fell, as well as the attack on the Pentagon in Washington, D.C. and the crashing of another plane near Shanksville, Pennsylvania.

As part of the memorial ceremony, the names of all 2,983 people killed in the attacks were read out.

Many relatives of loved ones walked around the two giant fountains that bear the names of all those who died at Ground Zero, placing flowers and small American flags at the inscriptions of names.