New York: The skyscraper being built on the site of New York City's September 11, 2001 terrorist attack has reached 100 floors, the project's owners announced. The building is most commonly known as the "Freedom Tower" but officially called "One World Trade Center."

"Steel installation for One World Trade Center has reached the 100th floor, with four more floors to go before it reaches the top of the tower," the Port Authority of New York and New Jersey said in a statement on Tuesday.

The Freedom Tower, scheduled to be opened in 2013, is being built to a height of 541 meters, which is a symbolic figure reminiscent of the US year of independence.

The glass walls have been built to the 70th floor while the concrete floors are poured to the 87th floor, the Port Authority of New York and New Jersey said on its website.

The building is planned to be the tallest in the United States when it is completed. The skyscraper is being built alongside the 9/11 Memorial, where the World Trade Center's Twin Towers stood until terrorists slammed airliners into them, killing nearly 3,000 people.