New York City and the nation paused at 1 p.m. for a collective moment of silence.
The agency that owns the World Trade Center site asked all Americans to participate.
The Port Authority of New York and New Jersey asked Sunday that people "cease all regular activity for one minute to reflect on the lives lost and those affected by the tragedies of 9/11."
At ground zero, New York marked a decade since the attacks with a ritual reading of the names and several moments of silence.
The ground zero ceremony paused for the moments exactly 10 years ago that the hijacked planes hit the towers and when they collapsed. The times that the other planes hit the Pentagon and crashed in Pennsylvania were also observed with silence.
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