Two people are dead and four are unaccounted for in a massive explosion in East Harlem that toppled two buildings. At least 17 people are injured.

Nearly 200 firefighters and emergency personnel are on scene at East 116th St. and Park Ave.

Witnesses say they heard a loud blast coming from a five-story building at about 9:30 a.m.

The residential building and a neighboring building with businesses on the ground level collapsed.

The NYPD bomb squad responded to the scene. There are reports there was a construction project underway in the impacted area.

A resident of the neighborhood tells FOX 5 News there was a strong smell of gas last night surrounding the building.

Con Edison has crews on the scene.

FIRST REPORT 10:00AM ET: The FDNY and NYPD are on the scene of an explosion inside a building on E. 116th St. in Manhattan. the building is a residential structure, and a collapse has been confirmed. There is also a working fire in the building. FDNy has requested a 3rd Alarm response, and the NYPD has called for a Level 2 Mobilization, which is a very large response of various emergency personnel.

Breaking911.com is reporting that Metro-North train traffic has been shut down on Park Ave, and that there is a serious gas leak at the location.

Unknown extent of injuries.

(Source: Breaking911.com)