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

The office building, located at 345 Park Avenue, houses some of the country’s top financial firms, including Blackstone, and the National Football League. According to the company's website, Blackstone stands as the world’s largest alternative asset manager, managing over $1 trillion in assets under management.

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.