Active Shooter Dead After Opening Fire in Manhattan, Multiple Victims

5:46 PM PT -- An off-duty police officer and at least four other people are dead from the shooting, law enforcement sources tell TMZ.

The gunman has been identified as 27-year-old Shane Tamura of Las Vegas according to our law enforcement sources.

Absolute mayhem in Manhattan ... there was an active shooter who injured multiple people before turning the gun on himself.

The New York Police Department tells TMZ ... officers got a call for shots fired Monday at 345 Park Avenue.

There are reports that one of the gunshot victims is a police officer and that the suspect was found dead from an apparent self inflicted gunshot wound.

Videos on social media show a massive police response ... cops are running towards the shooter and civilians are running for cover. There's also a ton of police vehicles and sirens ringing out.

Tenants at 345 Park Avenue, a skyscraper in Midtown Manhattan, include Blackstone, KPMG, J.P. Morgan and the NFL ... just to name a few.

The shooter reportedly entered the skyscraper with an assault rifle and a bulletproof vest and then barricaded himself on the 32nd floor. It's unclear if the shooting happened inside or outside the building.

Footage shows NYPD officers giving someone chest compressions on the street.

FBI deputy director Dan Bongino says agents are responding to the scene to provide support.

NYPD is telling people to avoid the area of East 52 Street between Park Avenue and Lexington Avenue.