But tensions only rose when, three hours after the blast, a second device was found four blocks away — a pressure cooker that an early investigation found was likely also a bomb.

“The bomb squad believes it’s real,” a police source with knowledge of the investigation told The Post of that second device, found at 27th Street between Sixth and Seventh avenues. The cooker was safely removed from the scene by NYPD.

The strength of the W. 23rd St. blast sent the Dumpster flying from the north side of the street to the south sidewalk, and it landed without hitting anyone or anything, police sources told The Post.