At 3:40 p.m., the FDNY responded to 55 Church Street, site of the Millenium Hilton hotel, for a report of falling glass.
A hotel spokeswoman says a piece of metal, about 1 foot by 1 foot, flew into the window of a guest room, causing it to break. It's not clear where the metal came from.
No one was in the room at the time, and no one was hurt.
A glass contractor headed to the hotel for repairs.
Dey Street was closed off to pedestrians and cars.
The hotel says it is fully cooperating with local authorities in the investigation.