NEW YORK -- While the U.S. contends with the destruction caused by two ferocious hurricanes in three weeks, Americans also are marking the 16th anniversary of one of the nation's most scarring days.

Thousands of 9/11 victims' relatives, survivors, rescuers and others gathered Monday at the World Trade Center to remember the deadliest terror attack on American soil.

Observances also take place at the Pentagon and the Flight 93 National Memorial near Shanksville, Pennsylvania.

Nearly 3,000 people died when hijacked planes slammed into the trade center, the Pentagon and a field near Shanksville on Sept. 11, 2001.

Republican President Donald Trump, a native New Yorker, observed the anniversary for the first time as the nation's leader. He participated in a moment of silence and also in an observance at the Pentagon.