A ribbon-cutting was held Wednesday for the 978-foot 4 World Trade Center. It stands near 1 World Trade Center, sometimes called the Freedom Tower. That tower was declared the nation's tallest this week and is expected to open next year.
Four World Trade is designed by Fumihiko Maki. It faces the Sept. 11 memorial's south reflecting pool.
The Port Authority of New York and New Jersey expects to move into 4 World Trade in 2015. The authority lost its home in the twin towers during the 2001 terror attacks.
The official opening means it can start building out its new office space.
Another office tower at 7 World Trade Center opened in 2006.