WATCH LIVE 9/11 anniversary: Ground Zero, Flight 93, Pentagon ceremonies

WATCH: Vice President Pence Speaks at Flight 93 memorial

It has been 18 years since nearly 3,000 people were killed when four planes were flown into New York City's World Trade Center, The Pentagon and into a field in Shanksville, Pennsylvania.

Ceremonies to mark the somber day will be held at all three locations.

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In New York, the ceremony will begin at the 9/11 Memorial plaza in Lower Manhattan at 8:39 a.m. EDT. And will consist of family members of those killed reading the names of each person who died on both 9/11 and during a previous attack on the World Trade Center in 1993, WABC reported. They will pause to mark the exact time each plane hit the towers, when the towers fell and the attack on the Pentagon occurred and Flight 93 crashed. The 9/11 Memorial Museum will be open only for victims' family members, WABC reported.

An addition has been made to the memorial to honor those who have died after the attacks due to the toxins that they were exposed to at Ground Zero. It's called the 9/11 Memorial Glade and is dedicated "to those whose actions in our time of need led to injury, sickness, and death," USA Today reported.

You can watch the ceremony here.

The Pentagon ceremony will begin with the unfurling of the American Flag on the side of the Pentagon at 6:46 a.m. EDT, the Department of Defense said in a press release. The memorial will be closed to the public so families of the 184 people who were killed can take part in a private ceremony. The memorial will reopen after 11 a.m. Wednesday. A moment of silence will be held in Washington at 9:37 a.m. to mark the time the plane hit the Pentagon, USA Today reported.

President Donald Trump is expected to speak at the Pentagon ceremony, The Hill reported.

You can watch that ceremony here.

Then on Monday, the memorial, which is normally open 24 hours a day, seven days a week, will be closed so repairs and construction can be done. The bench area will be the first to be closed to the public, with the Memorial Gateway entrance being closed Nov. 16, WRC reported.

The memorial service to honor those killed when Flight 93 crashed in Shanksville, Pennsylvania, will begin at 9:45 a.m. and the names of the 40 passengers and crew members killed will start being read, with a bell rung after each, to coincide with the time the plane crashed at 10:03 a.m. Vice President Mike Pence is speaking at the ceremony.