Ceremonies will be held at the World Trade Center, the Pentagon and at the crash site of Flight 93 in Shanksville, Pennsylvania.
On the 16th anniversary of 9/11, the U.S. government has released rare pictures that reveal the horror inside the building after it was hit by a American Airlines Flight 77.
Donald Trump has led tributes to the 9/11 victims on the 16th anniversary of the terror attacks, saying the United States grieves for the people "murdered by terrorists" in 2001.
Around the country, a remembrance ceremony will be held at the 9/11 Memorial Museum in NY.
There will also be six moments of silence with the fist at 8:46 a.m., when the first plane hit the north tower, and the next at 9:03 a.m., when the second plane struck the south tower.
Jose Jimenez/Primera Hora/Getty ImagesA survivor sits outside the World Trade Center after two planes hit the building September 11, 2001 in New York City.
Following the moment of silence at Ground Zero in NY, family members of the almost 3,000 people killed 16 years ago began reading out the names of those who died in the attacks.
Meanwhile, at Ground Zero in NY, victims' relatives marked the anniversary by reading out the names of those who died.
On Sept. 11, 2001, terrorists hijacked four passenger planes. The White House said he is to be joined by first lady Melania Trump.
Speaking at an observance at the Pentagon, the Republican president issued a warning to extremists, saying "America can not be intimidated".
Yet last year's 15th-anniversary ceremony became entangled in the narrative of a fractious presidential campaign when Democratic nominee Hillary Clinton left abruptly, stumbled into a van and ultimately revealed she'd been diagnosed days earlier with pneumonia.
After the names are read out at that ceremony, there will be a public observance with a wreath-laying and public addresses.