As a gunman rampaged through 345 Park Ave., an unthinkable nightmare unfolded for the thousands of employees who work at the landmark New York office tower, which is home to such firms as the private-equity giant Blackstone and KPMG, as well as the National Football League.

An active shooter incident occurred in Midtown Manhattan, New York, officials said. Here's what to know about 345 Park Ave.

Park Avenue is home to several high-profile tenants, making it one of the most prominent office addresses in Midtown Manhattan. The building serves as the global headquarters of Blackstone Group, occupying more than a million square feet across approximately 28 floors.

The deadly Park Avenue shooting happened at one of the the most exclusive addresses in Midtown Manhattan — the “Blackstone Building," which is home to financial giant Blackstone, the NFL and accounting firm KPMG among a slew of other corporate names.

The New York Police Department said shots were fired at the building that houses Blackstone, KPMG, and other businesses on Monday evening.