The FDNY says the crane's weight apparently shifted as the beam was being lifted to 4 World Trade Center at around 11:30 a.m. Wednesday. It hit windows on the 45th and 46th floors.
The incident happened at the building on Church Street and Liberty Avenue.
No injuries were reported. About 60 firefighters responded to the scene.
Authorities closed Church Street and Liberty Street, and Zuccotti Park was closed while glass and debris were removed. People were also moved from the September 11th Memorial.
John Gallagher, of Tishman Construction Corporation, released the following statement:
"A sudden gust of wind caused a steel load to impact a curtain wall panel on the south side of Tower 4. As a result, some pieces of glass fell onto Liberty Street. Fortunately, the street was closed at the time, and the Liberty Street sidewalk is protected by a construction shed. There are no reports of injuries. We have suspended steel lifts pending an investigation, are inspecting the entire facade of the building, and are reviewing protocols for evaluating weather conditions."
The final steel beam was set atop 4 World Trade earlier this week. The 72-story skyscraper is expected to be the first to open at the site since the twin towers were destroyed in 2001.