The incredible photographs had not been shared in 20 years before appearing on Flickr earlier this year.
The series shows the moments immediately after two passenger jets crashed into the World Trade Center towers in Manhattan, events which indelibly marked the pages of history and continue to have a huge impact on the world today.
The amazing images - taken from an apartment on Greenwich Street near to the towers - capture the smoking ruins of the building, as well as the collapse of the towers in shocking clarity.
Some show the dust-covered streets below the building, as well as the empty void left after the towers' collapse.
They were shared by Flickr user Liam E, who scanned in the photographs after remembering that his great aunt had taken them and passed them down through the family.
He captioned the photo album: "Photographs that a late relative of mine took from their 310 Greenwich Street apartment balcony in New York City, facing south, on Tuesday, September 11, 2001.
"These photos I possess, never before seen, capture one of the most influential events in modern history."
Speaking to LADbible, Liam explained: "The photos were taken by my late great aunt, Maryann Puglisi-Muñoz, who worked in the fashion industry.
"She took the photos from her Greenwich Street apartment balcony, looking south towards the World Trade Center.
"The photos were later given to my late grandmother - her sister - and then to my mom and me a few years ago.
"They sat untouched for years until February, when I recalled that we had them, and my mom brought out the photo book.
"I scanned them, posted them on the internet, and people grew interested in them!"
He added: "My immediate family has a bit of history related to 9/11.
"My mother, Lisa, had taken a Circle Line tour around Lower Manhattan a few weeks before 9/11 and my father, Frank, at the time worked for NBC as an audio engineer and would have been near the towers that day but declined after the North Tower was hit."
Fortunately, the members of Liam's family were not involved in the events of that day, when international terrorists claimed the lives of nearly 3,000 people.
However, the photos provide a stark reminder of the reality of the day, and stand as a tribute to those who weren't so lucky.
You can view the full album here.Featured Image Credit: Liam E/Flickr